SR protein kinases (SRPKs) phosphorylate Ser⁄Arg dipeptide-containing proteins that play crucial roles in a broad spectrum of basic cellular processes. Phosphorylation by SRPKs constitutes a major way of regulating such cellu-lar mechanisms. In the past, we have shown that SRPK1a interacts with the nuclear matrix protein scaffold attachment factor B1 (SAFB1) via its unique N-terminal domain, which differentiates it from SRPK1.