Function and regulation of a deubiquitinating enzyme module at the Golgi

Abstract

ABSTRACT Eukaryotic genes contain coding exons which are largely interspersed by non-coding introns. The splicing of precursor mRNAs into protein-coding mRNAs by the removal of introns is mediated by the large ribonucleoprotein complex called the spliceosome. Although the role of core splicing factors is well-characterized, the significance of specialized splicing regulators is not well understood. Sde2 is one such highly conserved regulator. It is a ubiquitin-fold-activated splicing regulator required for the efficient splicing of selected introns in a subset of genes in Schizosaccharomyces pombe. In the first part, we wanted to identify why only selected pre-mRNAs required Sde2 for its efficient splicing. By bioinformatic analysis and monitoring splicing-specific ura4 reporters, we identified that introns with longer spacing between branchpoint and 3’ss splice site (for example, ftp105 intron-3) required Sde2 for its proper splicing. We also found that ubiquitin-like processing is required for the proper activity of Sde2. Additional intron-specific splicing factors, Cay1 and Tls1 along with Sde2, regulate heterochromatin formation and telomeric silencing by ensuring the proper splicing of key heterochromatin factors. Thus, splicing of suboptimal introns with longer spacing between branchpoint and 3’ss required intron-specific splicing factors for its efficient splicing and this in turn regulates the formation of heterochromatin.