CDK-9/cyclin T (P-TEFb) is required in two postinitiation pathways for transcription in the C. elegans embryo.
The metazoan transcription elongation factor P-TEFb (CDK-9/cyclin T) is essential for HIV transcription, and is recruited by some cellular activators. P-TEFb promotes elongation in vitro by overcoming pausing that requires the SPT-4/SPT-5 complex, but considerable evidence indicates that SPT-4/SPT-5 facilitates elongation in vivo. Here we used RNA interference to investigate P-TEFb functions in vivo, in the Caenorhabditis elegans embryo. We found that P-TEFb is broadly essential for expression of early embryonic genes. P-TEFb is required for phosphorylation of Ser 2 of the RNA Polymerase II C-terminal domain (CTD) repeat, but not for most CTD Ser 5 phosphorylation, supporting the model that P-TEFb phosphorylates CTD Ser 2 during elongation. Remarkably, although heat shock genes are cdk-9-dependent, they can be activated when spt-4 and spt-5 expression is inhibited along with cdk-9. This observation suggests that SPT-4/SPT-5 has an inhibitory function in vivo, and that mutually opposing influences of P-TEFb and SPT-4/SPT-5 may combine to facilitate elongation, or insure fidelity of mRNA production. Other genes are not expressed when cdk-9, spt-4, and spt-5 are inhibited simultaneously, suggesting that these genes require P-TEFb in an additional mechanism, and that they and heat shock genes are regulated through different P-TEFb-dependent elongation pathways.
Shim
Eun Yong
EY
Center for Blood Research, Harvard Medical School, Boston, Massachusetts 02115, USA.
Walker
Amy K
AK
Shi
Yang
Y
Blackwell
T Keith
TK
D000818:Animals; D017173:Caenorhabditis elegans / Q000196:embryology*; D029742:Caenorhabditis elegans Proteins; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D008957:Models, Genetic; D009687:Nuclear Proteins / Q000378:metabolism; D010641:Phenotype; D010766:Phosphorylation; D042925:Positive Transcriptional Elongation Factor B; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism* / Q000502:physiology*; D012313:RNA / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D035602:Transcriptional Elongation Factors
D029742:Caenorhabditis elegans Proteins; C492142:DSIF protein, C elegans; D009687:Nuclear Proteins; C080991:SPT4 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D035602:Transcriptional Elongation Factors; D012313:RNA; D042925:Positive Transcriptional Elongation Factor B; D017346:Protein Serine-Threonine Kinases; D042863:Cyclin-Dependent Kinase 9; D018844:Cyclin-Dependent Kinases; C467968:cdk9 protein kinase, C elegans