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Human transcription co-regulator SNW1/SKIP modulates the activity of various transcription factors, the elongating complex of RNA-PolII, and the spliceosome, which suggests that SNW1/SKIP may link pre-mRNA splicing to other processes of gene expression. We identified temperature sensitive alleles of the yeast homolog of SNW1/SKIP, PRP45, which at permissive temperature elicit cell shape and cell division defects. Cwc2-TAP purified spliceosomal complexes from prp45(1-169) cells showed a decreased stoichiometry of Prp22, suggesting an aberrant association of the helicase with the spliceosome. Using a synthetic lethality screen, we isolated several alleles of PRP22 which genetically interact with the allele prp45(1-169). Splicing analysis in vivo showed that prp45(1-169) cells were less efficient in splicing of non-canonical substrates as compared to WT. The expression of Prp45(119-379) in prp45(1-169) cells restored Prp22 partition in the Cwc2-pulldowns and the splicing defects of prp45(1-169) strain. Data on splicing phenotypes of prp22 and prp45 alleles suggest that Prp45 co-modulates Prp22 in the spliceosome, contributing to splicing efficiency and proper stringency of splice site choice. This work was supported by the Czech Ministry of Education, Youth and Sports grants MSM0021620858 and LC07032. [ABSTRACT FROM AUTHOR]

Circadian clocks generate endogenous rhythms in most organisms from cyanobacteria to humans and facilitate entrainment to environmental diurnal cycles, thus conferring a fitness advantage. Both transcriptional and posttranslational mechanisms are prominent in the basic network architecture of circadian systems. Posttranscriptional regulation, including mRNA processing, is emerging as a critical step for clock function. However, little is known about the molecular mechanisms linking RNA metabolism to the circadian clock network. Here, we report that a conserved SNW/Ski-interacting protein (SKIP) domain protein, SKIP, a splicing factor and component of the spliceosome, is involved in posttranscriptional regulation of circadian clock genes in Arabidopsis thaliana. Mutation in SKIP lengthens the circadian period in a temperature-sensitive manner and affects light input and the sensitivity of the clock to light resetting. SKIP physically interacts with the spliceosomal splicing factor Ser/Arg-rich protein45 and associates with the pre-mRNA of clock genes, such as PSEUDORESPONSE REGULATOR7 (PRR7) and PRR9 , and is necessary for the regulation of their alternative splicing and mRNA maturation. Genome-wide investigations reveal that SKIP functions in regulating alternative splicing of many genes, presumably through modulating recognition or cleavage of 5′ and 3′ splice donor and acceptor sites. Our study addresses a fundamental question on how the mRNA splicing machinery contributes to circadian clock function at a posttranscriptional level. [ABSTRACT FROM AUTHOR]