Figure 10.

Model of phosphorylation of two subclasses of SR protein. A, after phosphorylation of SR protein that contains two RRMs, the presence of the pseudo-RRM prevents the phosphoryl content, at least transiently, from dephosphorylation by protein phosphatases. RS dipeptides colored in gray indicate that the C-terminal region, in the case of SRSF1, is regulated by a regiospecific mechanism and remains unphosphorylated. B, phosphorylation sites of single RRM–containing SR protein are accessible by phosphatases, allowing dynamic regulation of the phosphoryl content by both phosphatases and SRPK. A dashed arrow indicates that the dephosphorylated substrate may be subjected to rephosphorylation by SRPK.