Binding of the human papillomavirus E1 origin-recognition protein is regulated through complex formation with the E2 enhancer-binding protein.

CCAAT/enhancer-binding protein β (C/EBPβ) can function as a repressor or as an activator of human papillomavirus (HPV) gene expression, depending on which cell type the experiments are conducted. In this report, it was shown that within primary human foreskin keratinocyte cells (HFK) the activity of C/EBPβ can be switched from that of a repressor of HPV11 expression to an activator by mutating a single promoter-proximal consensus YY1-binding site within the HPV11 upstream regulatory region (URR). It was shown that in HFK cells, exogenous expression of C/EBPβ significantly activates the expression of mutant HPV11 URR reporter plasmids that contain deletions which overlap a 127 bp region (−269 to −142). Inclusive in this region are binding sites for multiple transcription factors, including AP1, YY1 and C/EBPα. Only mutation of the YY1 site resulted in the switch in phenotype, indicating that C/EBPβ represses HPV11 expression in these cells via YY1 binding. The level of YY1 activity was also measured in HFK cells transfected with a C/EBPβ expression plasmid and a significant increase in YY1 activity as compared with mock-transfected cells was found. C33A cells, which exhibit activation of wild-type HPV11 gene expression with exogenous C/EBPβ co-expression, failed to demonstrate C/EBPβ-induced YY1 activation. It was concluded that in HFK cells, exogenous C/EBPβ induces the activity of YY1, which, in turn, can repress HPV11 URR expression through the promoter-proximal YY1-binding site.

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Repressor Forms of the Enhancer-binding Protein NtrC: Some Fail in Coupling ATP Hydrolysis to Open Complex Formation by σ54-Holoenzyme

Journal of Molecular Biology ◽

10.1006/jmbi.1996.0403 ◽

1996 ◽

Vol 260 (3) ◽

pp. 317-331 ◽

Cited By ~ 38

Author(s):

Anne K. North ◽

David S. Weiss ◽

Hideyuki Suzuki ◽

Yehuda Flashner ◽

Sydney Kustu

Keyword(s):

Complex Formation ◽

Atp Hydrolysis ◽

Binding Protein ◽

Enhancer Binding Protein ◽

Open Complex Formation

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Nucleoprotein complex formation by the enhancer binding protein nifA

Nucleic Acids Research ◽

10.1093/nar/25.17.3478 ◽

1997 ◽

Vol 25 (17) ◽

pp. 3478-3485 ◽

Cited By ~ 14

Author(s):

X. Wang

Keyword(s):

Complex Formation ◽

Binding Protein ◽

Enhancer Binding Protein ◽

Nucleoprotein Complex

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Isolation and Properties of the Complex between the Enhancer Binding Protein NIFA and the Sensor NIFL

Journal of Bacteriology ◽

10.1128/jb.181.15.4461-4468.1999 ◽

1999 ◽

Vol 181 (15) ◽

pp. 4461-4468 ◽

Cited By ~ 44

Author(s):

Tracy Money ◽

Tamera Jones ◽

Ray Dixon ◽

Sara Austin

Keyword(s):

Complex Formation ◽

Azotobacter Vinelandii ◽

Binding Protein ◽

Protein Protein Interaction ◽

Amino Terminal ◽

Cell Extracts ◽

Enhancer Binding Protein ◽

Adenosine Nucleotides

ABSTRACT In Azotobacter vinelandii, activation ofnif gene expression by the transcriptional regulatory enhancer binding protein NIFA is controlled by the sensor protein NIFL in response to changes in levels of oxygen and fixed nitrogen in vivo. NIFL is a novel redox-sensing flavoprotein which is also responsive to adenosine nucleotides in vitro. Inhibition of NIFA activity by NIFL requires stoichiometric amounts of the two proteins, implying that the mechanism of inhibition is by direct protein-protein interaction rather than by catalytic modification of the NIFA protein. The formation of the inhibitory complex between NIFL and NIFA may be regulated by the intracellular ATP/ADP ratio. We show that adenosine nucleotides promote complex formation between purified NIFA and NIFL in vitro, allowing isolation of the NIFL-NIFA complex. The complex can also be isolated from cell extracts containing coexpressed NIFL and NIFA in the presence of MgADP. Removal of the nucleotide causes dissociation of the complex. Experiments with truncated proteins demonstrate that the amino-terminal domain of NIFA and the C-terminal region of NIFL potentiate the ADP-dependent stimulation of NIFL-NIFA complex formation.

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Protein-Protein Interactions in the Complex between the Enhancer Binding Protein NIFA and the Sensor NIFL fromAzotobacter vinelandii

Journal of Bacteriology ◽

10.1128/jb.183.4.1359-1368.2001 ◽

2001 ◽

Vol 183 (4) ◽

pp. 1359-1368 ◽

Cited By ~ 23

Author(s):

Tracy Money ◽

Jason Barrett ◽

Ray Dixon ◽

Sara Austin

Keyword(s):

Complex Formation ◽

Protein Interactions ◽

Azotobacter Vinelandii ◽

Protein Complexes ◽

Binding Protein ◽

Limited Proteolysis ◽

Regulatory System ◽

Terminal Domain ◽

Enhancer Binding Protein

ABSTRACT The enhancer binding protein NIFA and the sensor protein NIFL fromAzotobacter vinelandii comprise an atypical two-component regulatory system in which signal transduction occurs via complex formation between the two proteins rather than by the phosphotransfer mechanism, which is characteristic of orthodox systems. The inhibitory activity of NIFL towards NIFA is stimulated by ADP binding to the C-terminal domain of NIFL, which bears significant homology to the histidine protein kinase transmitter domains. Adenosine nucleotides, particularly MgADP, also stimulate complex formation between NIFL and NIFA in vitro, allowing isolation of the complex by cochromatography. Using limited proteolysis of the purified proteins, we show here that changes in protease sensitivity of the Q linker regions of both NIFA and NIFL occurred when the complex was formed in the presence of MgADP. The N-terminal domain of NIFA adjacent to the Q linker was also protected by NIFL. Experiments with truncated versions of NIFA demonstrate that the central domain of NIFA is sufficient to cause protection of the Q linker of NIFL, although in this case, stable protein complexes are not detectable by cochromatography.

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