Serine/Arginine Rich Splicing Factor 4 (SRSF4)

The apparent molecular mass of SRp75 is 75 kD; the phosphorylated SRp75 has a molecular mass of 57 kD. The authors found that SRp75, like other SR proteins, contains an N-terminal RNA recognition motif (RRM), a glycine-rich region, an internal region homologous to the RRM, and a long 315-amino acid C-terminal serine/arginine-rich domain.

These alternative splicing events target the resulting mRNAs for degradation by means of an RNA surveillance pathway called nonsense-mediated mRNA decay. Mouse orthologs of the human SR proteins exhibit the same unproductive splicing associated with conserved regions has arisen independently in different SR genes, suggesting that splicing factors may readily acquire this form of regulation.