scholarly journals Protolith affiliation and tectonometamorphic evolution of the Gurla Mandhata core complex, NW Nepal Himalaya

Geosphere ◽  
2021 ◽  
Author(s):  
Laurent Godin ◽  
Mark Ahenda ◽  
Djordje Grujic ◽  
Ross Stevenson ◽  
John Cottle
Keyword(s):  
Hanging Wall ◽  
Structural Data ◽  
Isotopic Analysis ◽  
Metamorphic Grade ◽  
Crustal Thickening ◽  
Main Central Thrust ◽  
Core Complex ◽  
The Core ◽  
Isotopic Analyses ◽  
High Metamorphic Grade

Assigning correct protolith to high metamorphic-grade core zone rocks of large hot orogens is a particularly important challenge to overcome when attempting to constrain the early stages of orogenic evolution and paleogeography of lithotectonic units from these orogens. The Gurla Mandhata core complex in NW Nepal exposes the Himalayan metamorphic core (HMC), a sequence of high metamorphic-grade gneiss, migmatite, and granite, in the hinterland of the Himalayan orogen. Sm-Nd isotopic analyses indicate that the HMC comprises Greater Himalayan sequence (GHS) and Lesser Himalayan sequence (LHS) rocks. Conventional interpretation of such provenance data would require the Main Central thrust (MCT) to be also outcropping within the core complex. However, new in situ U-Th/Pb monazite petrochronology coupled with petrographic, structural, and microstructural observations reveal that the core complex is composed solely of rocks in the hanging wall of the MCT. Rocks from the core complex record Eocene and late Oligocene to early Miocene monazite (re-)crystallization periods (monazite age peaks of 40 Ma, 25–19 Ma, and 19–16 Ma) overprinting pre- Himalayan Ordovician Bhimphedian metamorphism and magmatism (ca. 470 Ma). The combination of Sm-Nd isotopic analysis and U-Th/ Pb monazite petrochronology demonstrates that both GHS and LHS protolith rocks were captured in the hanging wall of the MCT and experienced Cenozoic Himalayan metamorphism during south-directed extrusion. Monazite ages do not record metamorphism coeval with late Miocene extensional core complex exhumation, suggesting that peak metamorphism and generation of anatectic melt in the core complex had ceased prior to the onset of orogen-parallel hinterland extension at ca. 15–13 Ma. The geometry of the Gurla Mandhata core complex requires significant hinterland crustal thickening prior to 16 Ma, which is attributed to ductile HMC thickening and footwall accretion of LHS protolith associated with a Main Himalayan thrust ramp below the core complex. We demonstrate that isotopic signatures such as Sm-Nd should be used to characterize rock units and structures across the Himalaya only in conjunction with supporting petrochronological and structural data.

scholarly journals The Timing of Metamorphism, Magmatism, and Cooling in the Zanskar, Garhwal, and Nepal Himalaya

1995 ◽  
Vol 11 ◽  
Author(s):  
M. P. Searle
Keyword(s):  
Hanging Wall ◽  
Crustal Thickening ◽  
Indian Plate ◽  
Eastern Himalaya ◽  
Normal Faults ◽  
The Tibetan Plateau ◽  
Main Central Thrust ◽  
Southern Tibet ◽  
Peak Metamorphism ◽  
Exhumation Rates

Following India-Asia collision, which is estimated at ca. 54-50 Ma in the Ladakh-southern Tibet area, crustal thickening and timing of peak metamorphism may have been diachronous both along the Himalaya (pre-40 Ma north Pakistan; pre-31 Ma Zanskar; pre-20 Ma east Kashmir, west Garhwal; 11-4 Ma Nanga Parbat) and cross the strike of the High Himalaya, propagating S (in Zanskar SW) with time. Thrusting along the base of the High Himalayan slab (Main Central Thrust active 21-19 Ma) was synchronous with N-S (in Zanskar NE-SW) extension along the top of the slab (South Tibet Detachment Zone). Kyanite and sillimanite gneisses in the footwall formed at pressure of 8-10 kbars and depths of burial of 28-35 km, 30- 21 Ma ago, whereas anchimetamorphic sediments along the hanging wall have never been buried below ca. 5-6 km. Peak temperatures may have reached 750 on the prograde part of the P-T path. Thermobarometers can be used to constrain depths of burial assuming a continental geothermal gradient of 28-30 °C/km and a lithostatic gradient of around 3.5-3.7 km/kbar (or 0.285 kbars/km). Timing of peak metamorphism cannot yet be constrained accurately. However, we can infer cooling histories derived from thermochronometers using radiogenic isotopic systems, and thereby exhumation rates. This paper reviews all the reliable geochronological data and infers cooling histories for the Himalayan zone in Zanskar, Garhwal, and Nepal. Exhumation rates have been far greater in the High Himalayan Zone (1.4-2.1 mm/year) and southern Karakoram (1.2-1.6 mm/year) than along the zone of collision (Indus suture) or along the north Indian plate margin. The High Himalayan leucogranites span 26-14 Ma in the central Himalaya, and anatexis occurred at 21-19 Ma in Zanskar, approximately 30 Ma after the collision. The cooling histories show that significant crustal thickening, widespread metamorphism, erosion and exhumation (and therefore, possibly significant topographic elevation) occurred during the early Miocene along the central and eastern Himalaya, before the strengthening of the Indian monsoon at ca. 8 Ma, before the major change in climate and vegetation, and before the onset of E-W extension on the Tibetan plateau. Exhumation, therefore, was primarily controlled by active thrusts and normal faults, not by external factors such as climate change.

scholarly journals Compressional origin of the Naxos metamorphic core complex, Greece: Structure, petrography, and thermobarometry

2019 ◽  
Vol 132 (1-2) ◽  
pp. 149-197 ◽  
Author(s):  
Thomas N. Lamont ◽  
Michael P. Searle ◽  
David J. Waters ◽  
Nick M.W. Roberts ◽  
Richard M. Palin ◽  
...  
Keyword(s):  
Regional Metamorphism ◽  
Shear Zones ◽  
Metamorphic Core Complex ◽  
Crustal Thickening ◽  
Normal Faults ◽  
Crustal Extension ◽  
Core Complex ◽  
The Core ◽  
History Of ◽  
Metamorphic Core

Abstract The island of Naxos, Greece, has been previously considered to represent a Cordilleran-style metamorphic core complex that formed during Cenozoic extension of the Aegean Sea. Although lithospheric extension has undoubtedly occurred in the region since 10 Ma, the geodynamic history of older, regional-scale, kyanite- and sillimanite-grade metamorphic rocks exposed within the core of the Naxos dome is controversial. Specifically, little is known about the pre-extensional prograde evolution and the relative timing of peak metamorphism in relation to the onset of extension. In this work, new structural mapping is presented and integrated with petrographic analyses and phase equilibrium modeling of blueschists, kyanite gneisses, and anatectic sillimanite migmatites. The kyanite-sillimanite–grade rocks within the core complex record a complex history of burial and compression and did not form under crustal extension. Deformation and metamorphism were diachronous and advanced down the structural section, resulting in the juxtaposition of several distinct tectono-stratigraphic nappes that experienced contrasting metamorphic histories. The Cycladic Blueschists attained ∼14.5 kbar and 470 °C during attempted northeast-directed subduction of the continental margin. These were subsequently thrusted onto the more proximal continental margin, resulting in crustal thickening and regional metamorphism associated with kyanite-grade conditions of ∼10 kbar and 600–670 °C. With continued shortening, the deepest structural levels underwent kyanite-grade hydrous melting at ∼8–10 kbar and 680–750 °C, followed by isothermal decompression through the muscovite dehydration melting reaction to sillimanite-grade conditions of ∼5–6 kbar and 730 °C. This decompression process was associated with top-to-the-NNE shearing along passive-roof faults that formed because of SW-directed extrusion. These shear zones predated crustal extension, because they are folded around the migmatite dome and are crosscut by leucogranites and low-angle normal faults. The migmatite dome formed at lower-pressure conditions under horizontal constriction that caused vertical boudinage and upright isoclinal folds. The switch from compression to extension occurred immediately following doming and was associated with NNE-SSW horizontal boudinage and top-to-the-NNE brittle-ductile normal faults that truncate the internal shear zones and earlier collisional features. The Naxos metamorphic core complex is interpreted to have formed via crustal thickening, regional metamorphism, and partial melting in a compressional setting, here termed the Aegean orogeny, and it was exhumed from the midcrust due to the switch from compression to extension at ca. 15 Ma.

scholarly journals Reconstitution of cargo-induced LC3 lipidation in mammalian selective autophagy

2021 ◽  
Vol 7 (17) ◽  
pp. eabg4922
Author(s):  
Chunmei Chang ◽  
Xiaoshan Shi ◽  
Liv E. Jensen ◽  
Adam L. Yokom ◽  
Dorotea Fracchiolla ◽  
...  
Keyword(s):  
Complex I ◽  
Kinase Activity ◽  
Protein Aggregates ◽  
Class Iii ◽  
Phosphatidylinositol 3 Kinase ◽  
Giant Unilamellar Vesicles ◽  
Core Complex ◽  
Selective Autophagy ◽  
The Core ◽  
Stimulation Of

Selective autophagy of damaged mitochondria, protein aggregates, and other cargoes is essential for health. Cargo initiates phagophore biogenesis, which entails the conjugation of LC3 to phosphatidylethanolamine. Current models suggest that clustered ubiquitin chains on a cargo trigger a cascade from autophagic cargo receptors through the core complexes ULK1 and class III phosphatidylinositol 3-kinase complex I, WIPI2, and the ATG7, ATG3, and ATG12ATG5-ATG16L1 machinery of LC3 lipidation. This was tested using giant unilamellar vesicles (GUVs), GST-Ub4 as a model cargo, the cargo receptors NDP52, TAX1BP1, and OPTN, and the autophagy core complexes. All three cargo receptors potently stimulated LC3 lipidation on GUVs. NDP52- and TAX1BP1-induced LC3 lipidation required all components, but not ULK1 kinase activity. However, OPTN bypassed the ULK1 requirement. Thus, cargo-dependent stimulation of LC3 lipidation is common to multiple autophagic cargo receptors, yet the details of core complex engagement vary between the different receptors.

Structural and geochronological constraints on the role of partial melting during the formation of the Shuswap metamorphic core complex at the latitude of the Thor-Odin dome, British Columbia

1999 ◽  
Vol 36 (6) ◽  
pp. 917-943 ◽  
Author(s):  
Olivier Vanderhaeghe ◽  
Christian Teyssier ◽  
Richard Wysoczanski
Keyword(s):  
Partial Melting ◽  
Metamorphic Core Complex ◽  
High Grade ◽  
Core Complex ◽  
Genetic Link ◽  
The Core ◽  
Lower Unit ◽  
Geochronological Constraints ◽  
Metamorphic Core ◽  
Middle Unit

At the latitude of the Thor-Odin dome, the Shuswap metamorphic core complex exposes a ~15 km thick structural section composed of an upper unit that preserved Mesozoic metamorphism, structures, and cooling ages, separated from the underlying high-grade rocks by low-angle detachment zones. Below the detachments, the core of the complex consists of an amphibolite-facies middle unit overlying a migmatitic lower unit exposed in the core of the Thor-Odin dome. Combined structural and super high resolution ion microprobe (SHRIMP) U-Pb geochronology studies indicate that the pervasive shallowly dipping foliation and east-west lineation developed in the presence of melt during Paleocene time. SHRIMP analyses of complexly zoned zircon grains suggest that the migmatites of the lower unit crystallized at ~56 Ma, and a syntectonic leucogranite at ~60 Ma. We suggest that leucogranite migrated upward from the migmatites through an array of dikes and sills that permeated the middle unit and ponded to form laccoliths spatially related to the detachment zones. The similarity in ages of inherited zircon cores in the two migmatite and the leucogranite samples suggests a genetic link consistent with the structural analysis. Following the crystallization of migmatites, the terrane cooled rapidly, as indicated by argon thermochronology. We propose that exhumation of the core of the Canadian Cordillera during the formation of the Shuswap metamorphic core complex occurred from ~60 to 56 Ma at a time when the crust was significantly partially molten. These structural and temporal relationships suggest a genetic link between mechanical weakening of the crust by partial melting, late-orogenic collapse, and exhumation of high-grade rocks in the hinterland of a thermally mature orogenic belt.

scholarly journals Synchrotron FTIR imaging of OH in quartz mylonites

Solid Earth ◽  
2017 ◽  
Vol 8 (5) ◽  
pp. 1025-1045 ◽  
Author(s):  
Andreas K. Kronenberg ◽  
Hasnor F. B. Hasnan ◽  
Caleb W. Holyoke III ◽  
Richard D. Law ◽  
Zhenxian Liu ◽  
...  
Keyword(s):  
Water Content ◽  
Point Defects ◽  
Fluid Inclusions ◽  
Hanging Wall ◽  
Molecular Water ◽  
Main Central Thrust ◽  
Absorption Bands ◽  
Uniform Equilibrium ◽  
Quartz Grains ◽  
Water Contents

Abstract. Previous measurements of water in deformed quartzites using conventional Fourier transform infrared spectroscopy (FTIR) instruments have shown that water contents of larger grains vary from one grain to another. However, the non-equilibrium variations in water content between neighboring grains and within quartz grains cannot be interrogated further without greater measurement resolution, nor can water contents be measured in finely recrystallized grains without including absorption bands due to fluid inclusions, films, and secondary minerals at grain boundaries.Synchrotron infrared (IR) radiation coupled to a FTIR spectrometer has allowed us to distinguish and measure OH bands due to fluid inclusions, hydrogen point defects, and secondary hydrous mineral inclusions through an aperture of 10 µm for specimens > 40 µm thick. Doubly polished infrared (IR) plates can be prepared with thicknesses down to 4–8 µm, but measurement of small OH bands is currently limited by strong interference fringes for samples < 25 µm thick, precluding measurements of water within individual, finely recrystallized grains. By translating specimens under the 10 µm IR beam by steps of 10 to 50 µm, using a software-controlled x − y stage, spectra have been collected over specimen areas of nearly 4.5 mm2. This technique allowed us to separate and quantify broad OH bands due to fluid inclusions in quartz and OH bands due to micas and map their distributions in quartzites from the Moine Thrust (Scotland) and Main Central Thrust (Himalayas).Mylonitic quartzites deformed under greenschist facies conditions in the footwall to the Moine Thrust (MT) exhibit a large and variable 3400 cm−1 OH absorption band due to molecular water, and maps of water content corresponding to fluid inclusions show that inclusion densities correlate with deformation and recrystallization microstructures. Quartz grains of mylonitic orthogneisses and paragneisses deformed under amphibolite conditions in the hanging wall to the Main Central Thrust (MCT) exhibit smaller broad OH bands, and spectra are dominated by sharp bands at 3595 to 3379 cm−1 due to hydrogen point defects that appear to have uniform, equilibrium concentrations in the driest samples. The broad OH band at 3400 cm−1 in these rocks is much less common. The variable water concentrations of MT quartzites and lack of detectable water in highly sheared MCT mylonites challenge our understanding of quartz rheology. However, where water absorption bands can be detected and compared with deformation microstructures, OH concentration maps provide information on the histories of deformation and recovery, evidence for the introduction and loss of fluid inclusions, and water weakening processes.

scholarly journals An anticlockwise metamorphic P-T path and nappe stacking in the Reisa Nappe Complex in the Scandinavian Caledonides, northern Norway: evidence for weakening of lower continental crust before and during continental collision

2018 ◽  
Author(s):  
Carly Faber ◽  
Holger Stünitz ◽  
Deta Gasser ◽  
Petr Jeřábek ◽  
Katrin Kraus ◽  
...  
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Large Scale ◽  
Structural Data ◽  
Geothermal Gradient ◽  
Continental Collision ◽  
Crustal Thickening ◽  
Northern Norway ◽  
Nappe Complex ◽  
T Path

Abstract. This study investigates the Caledonian metamorphic and tectonic evolution in northern Norway, examining the structure and tectonostratigraphy of the Reisa Nappe Complex (RNC; from bottom to top, Vaddas, Kåfjord and Nordmannvik nappes). Structural data, phase equilibrium modelling, and U-Pb zircon and titanite geochronology are used to constrain the timing and P-T conditions of deformation and metamorphism that formed the nappes and facilitated crustal thickening during continental collision. Five samples taken from different parts of the RNC reveal an anticlockwise P-T path attributed to the effects of early Silurian heating followed by thrusting. An early Caledonian S1 foliation in the Nordmannvik Nappe records kyanite-grade partial melting at ~ 760–790 °C and ~ 9.4–11 kbar. Leucosomes formed at 439 ± 2 Ma (U-Pb zircon) in fold axial planes in the Nordmannvik Nappe indicate that compressional deformation initiated while the rocks were still partially molten. This stage was followed by pervasive solid-state shearing as the rocks cooled and solidified, forming the S2 foliation at 680–730 °C and 9.5–10.9 kbar. Multistage titanite growth in the Nordmannvik Nappe records this extended metamorphism between 444 and 427 Ma. In the underlying Kåfjord Nappe, garnet cores record lower P-T (590–610 °C and 5.5–6.8 kbar) but a similar geothermal gradient as the S1 migmatitic event in the Nordmannvik Nappe, indicating formation at a higher relative position in the crust. S2 shearing in the Kåfjord Nappe occurred at 580–605 °C and 9.2–10.1 kbar, indicating a considerable pressure increase during nappe stacking. Gabbro intruded in the Vaddas Nappe at 439 ± 1 Ma, synchronously with migmatization in the Nordmannvik Nappe. In the Vaddas Nappe S2 shearing occurred at 630–640 ºC and 11.7–13 kbar. Titanite growth along the lower RNC boundary records S2-shearing at 432 ± 6 Ma. It emerges that early Silurian heating (~ 440 Ma), probably resulting from large-scale magma underplating, initiated partial melting that weakened the lower crust, which facilitated dismembering of the crust into individual nappe units. This tectonic style contrasts subduction of mechanically strong continental crust to great depths.

scholarly journals Anticlockwise metamorphic pressure–temperature paths and nappe stacking in the Reisa Nappe Complex in the Scandinavian Caledonides, northern Norway: evidence for weakening of lower continental crust before and during continental collision

Solid Earth ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 117-148 ◽  
Author(s):  
Carly Faber ◽  
Holger Stünitz ◽  
Deta Gasser ◽  
Petr Jeřábek ◽  
Katrin Kraus ◽  
...  
Keyword(s):  
Partial Melting ◽  
Continental Crust ◽  
Large Scale ◽  
Structural Data ◽  
Continental Collision ◽  
Crustal Thickening ◽  
Western Gneiss Region ◽  
Nappe Complex ◽  
T Path ◽  
Tectonic Style

Abstract. This study investigates the tectonostratigraphy and metamorphic and tectonic evolution of the Caledonian Reisa Nappe Complex (RNC; from bottom to top: Vaddas, Kåfjord, and Nordmannvik nappes) in northern Troms, Norway. Structural data, phase equilibrium modelling, and U-Pb zircon and titanite geochronology are used to constrain the timing and pressure–temperature (P–T) conditions of deformation and metamorphism during nappe stacking that facilitated crustal thickening during continental collision. Five samples taken from different parts of the RNC reveal an anticlockwise P–T path attributed to the effects of early Silurian heating (D1) followed by thrusting (D2). At ca. 439 Ma during D1 the Nordmannvik Nappe reached the highest metamorphic conditions at ca. 780 ∘C and ∼9–11 kbar inducing kyanite-grade partial melting. At the same time the Kåfjord Nappe was at higher, colder, levels of the crust ca. 600 ∘C, 6–7 kbar and the Vaddas Nappe was intruded by gabbro at > 650 ∘C and ca. 6–9 kbar. The subsequent D2 shearing occurred at increasing pressure and decreasing temperatures ca. 700 ∘C and 9–11 kbar in the partially molten Nordmannvik Nappe, ca. 600 ∘C and 9–10 kbar in the Kåfjord Nappe, and ca. 640 ∘C and 12–13 kbar in the Vaddas Nappe. Multistage titanite growth in the Nordmannvik Nappe records this evolution through D1 and D2 between ca. 440 and 427 Ma, while titanite growth along the lower RNC boundary records D2 shearing at 432±6 Ma. It emerges that early Silurian heating (ca. 440 Ma) probably resulted from large-scale magma underplating and initiated partial melting that weakened the lower crust, which facilitated dismembering of the crust into individual thrust slices (nappe units). This tectonic style contrasts with subduction of mechanically strong continental crust to great depths as seen in, for example, the Western Gneiss Region further south.

Accelerating exhumation in the Eocene North American Cordilleran hinterland: Implications from detrital zircon (U-Th)/(He-Pb) double dating

2019 ◽  
Vol 132 (1-2) ◽  
pp. 198-214 ◽  
Author(s):  
Andrew S. Canada ◽  
Elizabeth J. Cassel ◽  
Daniel F. Stockli ◽  
M. Elliot Smith ◽  
Brian R. Jicha ◽  
...  
Keyword(s):  
North American ◽  
Detrital Zircon ◽  
Sedimentary Basins ◽  
Metamorphic Core Complex ◽  
Crustal Thickening ◽  
Sediment Provenance ◽  
Core Complex ◽  
Extensional Faulting ◽  
Lag Times ◽  
Metamorphic Core

AbstractBasins in orogenic hinterlands are directly coupled to crustal thickening and extension through landscape processes and preserve records of deformation that are unavailable in footwall rocks. Following prolonged late Mesozoic–early Cenozoic crustal thickening and plateau construction, the hinterland of the Sevier orogen of western North America underwent late Cenozoic extension and formation of metamorphic core complexes. While the North American Cordillera is one of Earth’s best-studied orogens, estimates for the spatial and temporal patterns of initial extensional faulting differ greatly and thus limit understanding of potential drivers for deformation. We employed (U-Th)/(He-Pb) double dating of detrital zircon and (U-Th)/He thermochronology of detrital apatite from precisely dated Paleogene terrestrial strata to quantify the timing and magnitude of exhumation and explore the linkages between tectonic unroofing and basin evolution in northeastern Nevada. We determined sediment provenance and lag time evolution (i.e., the time between cooling and deposition, which is a measure of upper-crustal exhumation) during an 8 m.y. time span of deposition within the Eocene Elko Basin. Fluvial strata deposited between 49 and 45 Ma yielded Precambrian (U-Th)/He zircon cooling ages (ZHe) with 105–740 m.y. lag times dominated by unreset detrital ages, suggesting limited exhumation and Proterozoic through early Eocene sediment burial (&lt;4–6 km) across the region. Minimum nonvolcanic detrital ZHe lag times decreased to &lt;100 m.y. in 45–43 Ma strata and to &lt;10 m.y. in 43–41 Ma strata, illustrating progressive and rapid hinterland unroofing in Eocene time. Detrital apatite (U-Th)/He ages present in ca. 44 and 39 Ma strata record Eocene cooling ages with 1–20 m.y. lag times. These data reflect acceleration of basement exhumation rates by &gt;1 km/m.y., indicative of rapid, large-magnitude extensional faulting and metamorphic core complex formation. Contemporaneous with this acceleration of hinterland exhumation, syntectonic freshwater lakes developed in the hanging wall of the Ruby Mountains–East Humboldt Range metamorphic core complex at ca. 43 Ma. Volcanism driven by Farallon slab removal migrated southward across northeastern Nevada, resulting in voluminous rhyolitic eruptions at 41.5 and 40.1 Ma, and marking the abrupt end of fluvial and lacustrine deposition across much of the Elko Basin. Thermal and rheologic weakening of the lithosphere and/or partial slab removal likely initiated extensional deformation, rapidly unroofing deeper crustal levels. We attribute the observed acceleration in exhumation, expansion of sedimentary basins, and migrating volcanism across the middle Eocene to record the thermal and isostatic effects of Farallon slab rollback and subsequent removal of the lowermost mantle lithosphere.

scholarly journals Baculovirus Per Os Infectivity Factor Complex: Components and Assembly

2019 ◽  
Vol 93 (6) ◽  
Author(s):  
Xi Wang ◽  
Yu Shang ◽  
Cheng Chen ◽  
Shurui Liu ◽  
Meng Chang ◽  
...  
Keyword(s):  
Polyacrylamide Gel Electrophoresis ◽  
Critical Role ◽  
Previous Knowledge ◽  
Multiprotein Complex ◽  
Core Complex ◽  
Insect Midgut ◽  
Content Type ◽  
The Core ◽  
Liquid Chromatography Tandem Mass ◽  
The Impact

ABSTRACT Baculovirus entry into insect midgut cells is dependent on a multiprotein complex of per os infectivity factors (PIFs) on the envelopes of occlusion-derived virions (ODVs). The structure and assembly of the PIF complex are largely unknown. To reveal the complete members of the complex, a combination of blue native polyacrylamide gel electrophoresis, liquid chromatography-tandem mass spectrometry, and Western blotting was conducted on three different baculoviruses. The results showed that the PIF complex has a molecular mass of ∼500 kDa and consists of nine PIFs, including a newly discovered member (PIF9). To decipher the assembly process, each pif gene was knocked out from the Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV) genome individually by use of synthetic baculovirus technology, and the impact on PIF complex formation was investigated. Deletion of pif8 resulted in the formation of an ∼400-kDa subcomplex. Deletion of pif0, -4, -6, -7, or -9 resulted in a subcomplex of ∼230 kDa, but deletion of pif1, -2, or -3 abolished formation of any complex. Taken together, our data identified a core complex of ∼230 kDa, consisting of PIF1, -2, and -3. This revised the previous knowledge that the core complex was about 170 kDa and contained PIF1 to -4. Analysis of the PIF complex in cellular fractions suggested that it is assembled in the cytoplasm before being transported to the nucleus and subsequently incorporated into the envelopes of ODVs. Only the full complex, not the subcomplex, is resistant to proteolytic attack, indicating the essentiality of correct complex assembly for oral infection. IMPORTANCE Entry of baculovirus into host insects is mediated by a per os infectivity factor (PIF) complex on the envelopes of occlusion-derived viruses (ODVs). Knowledge of the composition and structure of the PIF complex is fundamental to understanding its mode of action. By using multiple approaches, we determined the complete list of proteins (nine) in the PIF complex. In contrast to previous knowledge in the field, the core complex is revised to ∼230 kDa and consists of PIF1 to -3 but not PIF4. Interestingly, our results suggest that the PIF complex is formed in the cytoplasm prior to its transport to the nucleus and subsequent incorporation into ODVs. Only the full complex is resistant to proteolytic degradation in the insect midgut, implying the critical role of the entire complex. These findings provide the baseline for future studies on the ODV entry mechanism mediated by the multiprotein complex.

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