HsRec2/Rad51L1, a Protein Influencing Cell Cycle Progression, Has Protein Kinase Activity

In complex with FKBP12, the immunosuppressant rapamycin binds to and inhibits the yeast TOR1 and TOR2 proteins and the mammalian homologue mTOR/FRAP/RAFT1. The TOR proteins promote cell cycle progression in yeast and human cells by regulating translation and polarization of the actin cytoskeleton. A C-terminal domain of the TOR proteins shares identity with protein and lipid kinases, but only one substrate (PHAS-I), and no regulators of the TOR-signaling cascade have been identified. We report here that yeast TOR1 has an intrinsic protein kinase activity capable of phosphorylating PHAS-1, and this activity is abolished by an active site mutation and inhibited by FKBP12-rapamycin or wortmannin. We find that an intact TOR1 kinase domain is essential for TOR1 functions in yeast. Overexpression of a TOR1 kinase-inactive mutant, or of a central region of the TOR proteins distinct from the FRB and kinase domains, was toxic in yeast, and overexpression of wild-type TOR1 suppressed this toxic effect. Expression of the TOR-toxic domain leads to a G1 cell cycle arrest, consistent with an inhibition of TOR function in translation. Overexpression of the PLC1gene, which encodes the yeast phospholipase C homologue, suppressed growth inhibition by the TOR-toxic domains. In conclusion, our findings identify a toxic effector domain of the TOR proteins that may interact with substrates or regulators of the TOR kinase cascade and that shares sequence identity with other PIK family members, including ATR, Rad3, Mei-41, and ATM.

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Requirement for Protein Kinase C θ for Cell Cycle Progression and Formation of Actin Stress Fibers and Filopodia in Vascular Endothelial Cells

Journal of Biological Chemistry ◽

10.1074/jbc.272.45.28704 ◽

1997 ◽

Vol 272 (45) ◽

pp. 28704-28711 ◽

Cited By ~ 66

Author(s):

Shaoqing Tang ◽

Kathleen G. Morgan ◽

Christopher Parker ◽

J. Anthony Ware

Keyword(s):

Cell Cycle ◽

Endothelial Cells ◽

Protein Kinase C ◽

Protein Kinase ◽

Cell Cycle Progression ◽

Vascular Endothelial Cells ◽

Stress Fibers ◽

Vascular Endothelial ◽

Cycle Progression ◽

Kinase C

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The Saccharomyces cerevisiae YAK1 gene encodes a protein kinase that is induced by arrest early in the cell cycle.

Molecular and Cellular Biology ◽

10.1128/mcb.11.8.4045 ◽

1991 ◽

Vol 11 (8) ◽

pp. 4045-4052 ◽

Cited By ~ 86

Author(s):

S Garrett ◽

M M Menold ◽

J R Broach

Keyword(s):

Cell Cycle ◽

Protein Kinase ◽

Kinase Activity ◽

Specific Activity ◽

S Phase ◽

Protein Kinase Activity ◽

Dependent Protein Kinase ◽

Protein Levels ◽

Cycle Arrest ◽

Dependent Protein

Null mutations in the gene YAK1, which encodes a protein with sequence homology to known protein kinases, suppress the cell cycle arrest phenotype of mutants lacking the cyclic AMP-dependent protein kinase (A kinase). That is, loss of the YAK1 protein specifically compensates for loss of the A kinase. Here, we show that the protein encoded by YAK1 has protein kinase activity. Yak1 kinase activity is low during exponential growth but is induced at least 50-fold by arrest of cells prior to the completion of S phase. Induction is not observed by arrest at stages later in the cell cycle. Depending on the arrest regimen, induction can occur either by an increase in Yak1 protein levels or by an increase in Yak1 specific activity. Finally, an increase in Yak1 protein levels causes growth arrest of cells with attenuated A kinase activity. These results suggest that Yak1 acts in a pathway parallel to that of the A kinase to negatively regulate cell proliferation.

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Molecular Evolution Allows Bypass of the Requirement for Activation Loop Phosphorylation of the Cdc28 Cyclin-Dependent Kinase

Molecular and Cellular Biology ◽

10.1128/mcb.18.5.2923 ◽

1998 ◽

Vol 18 (5) ◽

pp. 2923-2931 ◽

Cited By ~ 33

Author(s):

Frederick R. Cross ◽

Kristi Levine

Keyword(s):

Cell Cycle ◽

Biological Activity ◽

Cell Cycle Progression ◽

Dna Amplification ◽

Protein Kinase Activity ◽

Activation Loop ◽

Cyclin Dependent Kinase ◽

High Biological Activity ◽

Cycle Progression ◽

Growth Defects

ABSTRACT Many protein kinases are regulated by phosphorylation in the activation loop, which is required for enzymatic activity. Glutamic acid can substitute for phosphothreonine in some proteins activated by phosphorylation, but this substitution (T169E) at the site of activation loop phosphorylation in the Saccharomyces cerevisiae cyclin-dependent kinase (Cdk) Cdc28p blocks biological function and protein kinase activity. Using cycles of error-prone DNA amplification followed by selection for successively higher levels of function, we identified mutant versions of Cdc28p-T169E with high biological activity. The enzymatic and biological activity of the mutant Cdc28p was essentially normally regulated by cyclin, and the mutants supported normal cell cycle progression and regulation. Therefore, it is not a requirement for control of the yeast cell cycle that Cdc28p be cyclically phosphorylated and dephosphorylated. TheseCDC28 mutants allow viability in the absence of Cak1p, the essential kinase that phosphorylates Cdc28p-T169, demonstrating that T169 phosphorylation is the only essential function of Cak1p. Some growth defects remain in suppressed cak1 cdc28 strains carrying the mutant CDC28 genes, consistent with additional nonessential roles for CAK1.

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Ras controls growth, survival and differentiation in the Drosophila eye by different thresholds of MAP kinase activity

Development ◽

10.1242/dev.128.9.1687 ◽

2001 ◽

Vol 128 (9) ◽

pp. 1687-1696 ◽

Cited By ~ 3

Author(s):

K. Halfar ◽

C. Rommel ◽

H. Stocker ◽

E. Hafen

Keyword(s):

Cell Cycle ◽

Cell Cycle Progression ◽

Kinase Activity ◽

Photoreceptor Cells ◽

Loss Of Function ◽

Cellular Functions ◽

Partial Loss ◽

Cycle Progression ◽

Mapk Activity ◽

Dividing Cells

Ras mediates a plethora of cellular functions during development. In the developing eye of Drosophila, Ras performs three temporally separate functions. In dividing cells, it is required for growth but is not essential for cell cycle progression. In postmitotic cells, it promotes survival and subsequent differentiation of ommatidial cells. In the present paper, we have analyzed the different roles of Ras during eye development by using molecularly defined complete and partial loss-of-function mutations of Ras. We show that the three different functions of Ras are mediated by distinct thresholds of MAPK activity. Low MAPK activity prolongs cell survival and permits differentiation of R8 photoreceptor cells while high or persistent MAPK activity is sufficient to precociously induce R1-R7 photoreceptor differentiation in dividing cells.

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