SR-related proteins and the processing of messenger RNA precursors

The processing of messenger RNA precursors (pre-mRNA) to mRNA in metazoans requires a large number of proteins that contain domains rich in alternatin g arginine and serine residues (RS domains). These include members of the S R family of splicing factors and proteins that are structurally and functio nally distinct from the SR family, collectively referred to below as SR-rel ated proteins. Both groups of RS domain proteins function in constitutive a nd regulated pre-mRNA splicing. Recently, several SR-related proteins have been identified that are associated with the transcriptional machinery. Oth er SR-related proteins are associated with mRNA 3' end formation and have b een implicated in export. We review these findings and evidence that protei ns containing RS domains may play a fundamental role in coordinating differ ent steps in the synthesis and processing of pre-mRNA.