RESUMO
Glc7, the yeast protein phosphatase 1, is a component of the cleavage and polyadenylation factor (CPF). Here we show that downregulation of Glc7, or its dissociation from CPF in the absence of CPF subunits Ref2 or Swd2, results in similar snoRNA termination defects. Overexpressing a C-terminal fragment of Sen1, a superfamily I helicase required for snoRNA termination, suppresses the growth and termination defects associated with loss of Swd2 or Ref2, but not Glc7. Suppression by Sen1 requires nuclear localization and direct interaction with Glc7, which can dephosphorylate Sen1 in vitro. The suppressing fragment, and in a similar manner full-length Sen1, copurifies with the snoRNA termination factors Nrd1 and Nab3, suggesting loss of Glc7 from CPF can be compensated by recruiting Glc7 to Nrd1-Nab3 through Sen1. Swd2 is also a subunit of the Set1c histone H3K4 methyltransferase complex and is required for its stability and optimal methyltransferase activity.
Assuntos
Fosfoproteínas Fosfatases/metabolismo , Subunidades Proteicas/metabolismo , RNA Nucleolar Pequeno/genética , Proteínas de Saccharomyces cerevisiae/metabolismo , Transcrição Gênica , Fatores de Poliadenilação e Clivagem de mRNA/metabolismo , Morte Celular/fisiologia , DNA Helicases , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Proteínas Fúngicas/genética , Proteínas Fúngicas/metabolismo , Histona-Lisina N-Metiltransferase/genética , Histona-Lisina N-Metiltransferase/metabolismo , Complexos Multiproteicos/química , Complexos Multiproteicos/metabolismo , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Fosfoproteínas Fosfatases/genética , Proteína Fosfatase 1 , Subunidades Proteicas/genética , RNA Helicases , Splicing de RNA , RNA Nucleolar Pequeno/metabolismo , Proteínas de Ligação a RNA/genética , Proteínas de Ligação a RNA/metabolismo , Ribonucleoproteínas/genética , Ribonucleoproteínas/metabolismo , Saccharomyces cerevisiae/genética , Saccharomyces cerevisiae/metabolismo , Proteínas de Saccharomyces cerevisiae/genética , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Fatores de Poliadenilação e Clivagem de mRNA/química , Fatores de Poliadenilação e Clivagem de mRNA/genéticaRESUMO
The carboxy-terminal domain (CTD) of the RNA polymerase II (RNApII) largest subunit consists of multiple heptapeptide repeats with the consensus sequence YSPTSPS. Different CTD phosphorylation patterns act as recognition sites for the binding of various messenger RNA processing factors, thereby coupling transcription and mRNA processing. Polyadenylation factors are co-transcriptionally recruited by phosphorylation of CTD serine 2 (ref. 2) and these factors are also required for transcription termination. RNApII transcribes past the poly(A) site, the RNA is cleaved by the polyadenylation machinery, and the RNA downstream of the cleavage site is degraded. Here we show that Rtt103 and the Rat1/Rai1 5' --> 3' exonuclease are localized at 3' ends of protein coding genes. In rat1-1 or rai1Delta cells, RNA 3' to polyadenylation sites is greatly stabilized and termination defects are seen at many genes. These findings support a model in which poly(A) site cleavage and subsequent degradation of the 3'-downstream RNA by Rat1 trigger transcription termination.
Assuntos
Exorribonucleases/metabolismo , Regulação Fúngica da Expressão Gênica , RNA Polimerase II/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/enzimologia , Saccharomyces cerevisiae/genética , Transcrição Gênica , Imunoprecipitação da Cromatina , Exorribonucleases/genética , Mutação/genética , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Análise de Sequência com Séries de Oligonucleotídeos , Fosforilação , Poli A/genética , Poli A/metabolismo , Poliadenilação , Processamento Pós-Transcricional do RNA , RNA Fúngico/genética , RNA Fúngico/metabolismo , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Proteínas de Ligação a RNA , Proteínas de Saccharomyces cerevisiae/genéticaRESUMO
Bromodomain factor 1 (Bdf1) associates with Saccharomyces cerevisiae TFIID and corresponds to the C-terminal half of higher eukaryotic TAF1. It also associates with the SWR-C complex, which is important for Htz1 deposition. Bdf1 binds preferentially to acetylated histone H4. Bdf1 is phosphorylated, but the mechanism and significance of this modification have been unclear. Two distinct regions within Bdf1 are phosphorylated; one is just C terminal to the bromodomains and the other is near the C terminus. Mutational analysis shows that phosphorylation is necessary for Bdf1 function in vivo. Endogenous protein kinase CK2 purifies with Bdf1 and phosphorylates both domains. A similar mechanism may be responsible for phosphorylation of the C-terminal region of mammalian TAF1. These findings suggest that CK2 phosphorylation of Bdf1 may regulate RNA polymerase II transcription and/or chromatin structure.
Assuntos
Proteínas Serina-Treonina Quinases/metabolismo , Proteínas de Saccharomyces cerevisiae/metabolismo , Fatores de Transcrição/metabolismo , Caseína Quinase II , Fosforilação , Saccharomyces cerevisiae/metabolismo , Fator de Transcrição TFIID/metabolismoRESUMO
Messenger RNA 3'-end formation is functionally coupled to transcription by RNA polymerase II. By tagging and purifying Ref2, a non-essential protein previously implicated in mRNA cleavage and termination, we isolated a multiprotein complex, holo-CPF, containing the yeast cleavage and polyadenylation factor (CPF) and six additional polypeptides. The latter can form a distinct complex, APT, in which Pti1, Swd2, a type I protein phosphatase (Glc7), Ssu72 (a TFIIB and RNA polymerase II-associated factor), Ref2, and Syc1 are associated with the Pta1 subunit of CPF. Systematic tagging and purification of holo-CPF subunits revealed that yeast extracts contain similar amounts of CPF and holo-CPF. By purifying holo-CPF from strains lacking Ref2 or containing truncated subunits, subcomplexes were isolated that revealed additional aspects of the architecture of APT and holo-CPF. Chromatin immunoprecipitation was used to localize Ref2, Ssu72, Pta1, and other APT subunits on small nucleolar RNA (snoRNA) genes and primarily near the polyadenylation signals of the constitutively expressed PYK1 and PMA1 genes. Use of mutant components of APT revealed that Ssu72 is important for preventing readthrough-dependent expression of downstream genes for both snoRNAs and polyadenylated transcripts. Ref2 and Pta1 similarly affect at least one snoRNA transcript.
