P-TEFb kinase recruitment and function at heat shock loci.
P-TEFb, a heterodimer of the kinase Cdk9 and cyclin T, was isolated as a factor that stimulates formation of productive transcription elongation complexes in vitro. Here, we show that P-TEFb is located at >200 distinct sites on Drosophila polytene chromosomes. Upon heat shock, P-TEFb, like the regulatory factor HSF, is rapidly recruited to heat shock loci, and this recruitment is blocked in an HSF mutant. Yet, HSF binding to DNA is not sufficient to recruit P-TEFb in vivo, and HSF and P-TEFb immunostainings within a heat shock locus are not coincident. Insight to the function of P-TEFb is offered by experiments showing that the direct recruitment of a Gal4-binding domain P-TEFb hybrid to an hsp70 promoter in Drosophila cells is sufficient to activate transcription in the absence of heat shock. Analyses of point mutants show this P-TEFb stimulation is dependent on Cdk9 kinase activity and on Cdk9's interaction with cyclin T. These results, coupled with the frequent colocalization of P-TEFb and the hypophosphorylated form of RNA polymerase II (Pol II) found at promoter-pause sites, support a model in which P-TEFb acts to stimulate promoter-paused Pol II to enter into productive elongation.
Lis
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JT
Department of Molecular Biology and Genetics, Biotechnology Building, Cornell University, Ithaca, New York 14853, USA. JTL10@cornell.edu
Mason
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Peng
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J
Price
D H
DH
Werner
J
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D000818:Animals; D002460:Cell Line; D002874:Chromosome Mapping; D056906:Cyclin T; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D019281:Dimerization; D029721:Drosophila Proteins; D004331:Drosophila melanogaster / Q000235:genetics*; D005786:Gene Expression Regulation; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics*; D006358:Hot Temperature; D010766:Phosphorylation; D042925:Positive Transcriptional Elongation Factor B; D017346:Protein Serine-Threonine Kinases / Q000235:genetics* / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012469:Salivary Glands / Q000502:physiology; D014158:Transcription, Genetic; D014162:Transfection
C503687:CycT protein, Drosophila; D056906:Cyclin T; D016213:Cyclins; D029721:Drosophila Proteins; D018840:HSP70 Heat-Shock Proteins; D011994:Recombinant Proteins; D042925:Positive Transcriptional Elongation Factor B; D017346:Protein Serine-Threonine Kinases; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases