Figure 1.

Identification of Stk23/Srpk3 as a novel SRPK. (a) Microarray analysis was performed using the hearts of E9.0 Mef2c-null and wild-type embryos. Down-regulation of the Stk23/Srpk3 expression in the Mef2c-null hearts was confirmed by RT–PCR. (Gapd) Glyceraldehyde-3-phosphate dehydrogenase expression as a control. (b) Amino acid structure of mouse Stk23/Srpk3. Srpk3 is a 566-amino-acid protein that contains a bipartite kinase domain (underlined), N terminus, and a hinge region. (c) Schematic representation of mouse SRPK family kinases. Srpk3 shows high sequence similarity to Srpk1 and Srpk2 in the kinase domain, but not in the N terminus and hinge region. The percentages in the boxes are identities of Srpk1 and Srpk2 to Srpk3 at an amino acid level. Srpk3 and Srpk2 have serine- and proline-rich sequences in the N terminus, respectively. Amino acid numbers are also shown. (d) Phosphorylation assays using SR domain proteins. Srpk3 phosphorylated SF2/ASF and the N-terminal region of Lamin B Receptor (LBR) in vitro.