Distinctive features of Drosophila alternative splicing factor RS domain: Implication for specific phosphorylation, shuttling, and splicing activation

The human splicing factor 2, also called human alternative splicing factor (hASF), is the prototype of the highly conserved SR protein family involved in constitutive and regulated splicing of metazoan mRNA precursors. Here w e report that the Drosophila homologue of hASF (dASF) lacks eight repeating arginine-serine dipeptides at its carboxyl-terminal region (RS domain), pr eviously shown to be important for both localization and splicing activity of hASF. While this difference has no effect on dASF localization, it imped es its capacity to shuttle between the nucleus and cytoplasm and abolishes its phosphorylation by SR protein kinase 1 (SRPK1). dASF also has an altere d splicing activity. While being competent for the regulation of 5' alterna tive splice site choice and activation of specific splicing enhancers, dASF fails to complement S100-cytoplasmic splicing-deficient extracts. Moreover , targeted overexpression of dASF in transgenic flies leads to higher delet erious developmental defects than hASF overexpression, supporting the notio n that the distinctive structural features at the RS domain between the two proteins are likely to be functionally relevant in vivo.