Specific combinations of SR proteins associate with single pre-messenger RNAs in vivo and contribute different functions

Abstract

Serine/arginine-rich (SR) proteins are required for messenger RNA (mRNA) processing, export, surveillance, and translation. We show that in Chironomus tentans, nascent transcripts associate with multiple types of SR proteins in specific combinations. Alternative splicing factor (ASF)/SF2, SC35, 9G8, and hrp45/SRp55 are all present in Balbiani ring (BR) pre-messenger ribonucleoproteins (mRNPs) preferentially when introns appear in the pre-mRNA and when cotranscriptional splicing takes place. However, hrp45/SRp55 is distributed differently in the pre-mRNPs along the gene compared with ASF/SF2, SC35, and 9G8, suggesting functional differences. All four SR proteins are associated with the BR mRNPs during export to the cytoplasm. Interference with SC35 indicates that SC35 is important for the coordination of splicing, transcription, and 3′ end processing and also for nucleocytoplasmic export. ASF/SF2 is associated with polyribosomes, whereas SC35, 9G8, and hrp45/SRp55 cosediment with monoribosomes. Thus, individual endogenous pre-mRNPs/mRNPs bind multiple types of SR proteins during transcription, and these SR proteins accompany the mRNA and play different roles during the gene expression pathway in vivo.

Perichromatin Fibrils Accumulation in Hepatocyte Nuclei Reveals Alterations of Pre-mRNA Processing During Aging

“…After longer incubations, BrU amounts on PF of adult and old animals become similar: this could be due to the saturation of all labeling sites, but it could also suggest a slow down of PF processing and=or transport in old animals that would imply the persistence in the nucleoplasm of BrU-labeled pre-mRNA. The latter hypothesis is supported by the lower amounts of labeling for nucleoplasmic splicing factors found in old rats; in fact, in spite of the higher amounts of PF in old rats, snRNPs, involved in the early pre-mRNA splicing (Lü hrmann et al, 1990), are similar to adult animals, and SC-35, required not only for spliceosome assembly (Fu and Maniatis, 1990) but also for transcription, 3 0 end processing, and nucleuscytoplasmic export (Lin et al, 2008;Bjork et al, 2009), is even less abundant. Again, the nucleoplasmic decrease of anti-SC-35 labeling is accompanied by a parallel increase in IG, suggesting a diminished request on the transcription sites of this splicing factor, usually stored in IG (Fu and Maniatis, 1990).…”

SR proteins are NXF1 adaptors that link alternative RNA processing to mRNA export

“…Our previous work in P19 cells showed that individual SR proteins interact with distinct sets of mRNAs (Änkö et al 2010), suggesting that specific mRNAs may be controlled by SR protein family members independently (Björk et al 2009;Pandit et al 2013;Bradley et al 2015). Depletion of export adaptors usually causes only a modest export block due to functional substitution (Hautbergue et al 2009;Katahira et al 2009;Uranishi et al 2009).…”

Cyclin-Dependent Kinase 12 Increases 3′ End Processing of Growth Factor-Induced c-FOS Transcripts

“…Given that the EJC and SRSFs associate extensively with mRNA (43,53,59,69), we also performed RNA immunoprecipitations to determine the relative enrichment of CDK12 on c-FOS transcripts (Fig. 5B).…”