Function and mechanism of the unconventional ubiquitin like protein Hub1

Abstract

Ubiquitin-like proteins (UBLs) control various cellular processes such as protein newlinedegradation, DNA repair, autophagy, transcription, RNA splicing, and immune newlineresponses. Hub1 is one such UBLs that have been reported to regulate pre-mRNA newlinesplicing. However, the function and the mechanism of Hub1 in intron-rich eukaryotes newlinehas not been studied yet. We aimed to understand the role of Hub1 in RNA splicing newlinein an intron-rich unicellular eukaryote Schizosaccharomyces pombe, and a newlinemulticellular eukaryote, Caenorhabditis elegans. This study demonstrates a newlineconserved genome-wide role of Hub1 in pre-mRNA splicing in S. pombe. Hub1 alters newlinethe protein composition of the spliceosome selectively. It promotes splicing of pre- newlinemRNAs that are synthesized faster. It is likely that rapidly synthesizing transcripts newlinerequire Hub1 to couple transcription with splicing. We identified a functionally newlineconserved Hub1 surface centered at two positively charged residues critical for newlinesplicing in S. pombe. We also show that Hub1 directly binds to the Kreb s cycle newlineenzyme, Fum1, through another surface. This Hub1 surface also regulates pre- newlinemRNA splicing. Additionally, our study showed the potential role of Hub1 in trans- newlinesplicing in the multicellular C. elegans. In summary, Hub1 employs multiple surfaces newlineto facilitate binding of specific factors for its function in pre-mRNA splicing. My newlinefindings are highly relevant not only for regulatory and tissue-specific gene newlineexpression, but also for understanding new mechanisms of alternative splicing.