Smicl is required for phosphorylation of RNA polymerase II and affects 3'-end processing of RNA at the midblastula transition in Xenopus.
Smicl (Smad-interacting CPSF 30-like) is an unusual protein that interacts with transcription factors as well as with the cleavage and polyadenylation specificity factor (CPSF). Previous work has shown that Smicl is expressed maternally in the Xenopus embryo and is later required for transcription of Chordin. In this paper we search for additional targets of Smicl. We identify many genes whose onset of expression at the midblastula transition (MBT) requires Smicl and is correlated with the translocation of Smicl from cytoplasm to nucleus. At least one such gene, Xiro1, is regulated via 3'-end processing. In searching for a general mechanism by which Smicl might regulate gene expression at the MBT, we have discovered that it interacts with the tail of Rpb1, the largest subunit of RNA polymerase II. Our results show that Smicl is required for the phosphorylation of the Rpb1 tail at serine 2 of the repeated heptapeptide YSPTSPS. This site becomes hyperphosphorylated at the MBT, thus allowing the docking of proteins required for elongation of transcription and RNA processing. Our work links the onset of zygotic gene expression in the Xenopus embryo with the translocation of Smicl from cytoplasm to nucleus, the phosphorylation of Rpb1 and the 3'-end processing of newly transcribed mRNAs.
Collart
Clara
C
Wellcome Trust/CR-UK Gurdon Institute and Department of Zoology, University of Cambridge, Cambridge, UK.
Ramis
Joana M
JM
Down
Thomas A
TA
Smith
James C
JC
D021581:Active Transport, Cell Nucleus; D000818:Animals; D036703:Blastula / Q000378:metabolism*; D002460:Cell Line; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D009419:Nerve Tissue Proteins / Q000235:genetics; D010766:Phosphorylation; D026723:Polyadenylation; D011485:Protein Binding; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D026721:RNA 3' End Processing; D012319:RNA Polymerase II / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics; D014158:Transcription, Genetic; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis / Q000196:embryology* / Q000235:genetics / Q000378:metabolism*
D009419:Nerve Tissue Proteins; D021122:Protein Subunits; D014157:Transcription Factors; D029867:Xenopus Proteins; C484675:Xiro1 protein, Xenopus; C506006:ZC3H3 protein, Xenopus; D012319:RNA Polymerase II