| SRPK 1 and LBR protein kinases show identical substrate specificities . ^^^ Two SR Protein specific Kinases , SRPK 1 and SRPK 2 , have been shown to phosphorylate specifically the RS motifs of the SR family of splicing factors and play an important role in regulating both the spliceosome assembly and their intranuclear distribution , whereas an LBR associated kinase , that specifically phosphorylates a stretch of RS repeats located at the NH 2 terminal region of LBR , has been recently purified and characterized from turkey erythrocyte nuclear envelopes . ^^^ Using synthetic peptides representing different regions of LBR and recombinant proteins produced in bacteria we now demonstrate that SRPK 1 modifies LBR with similar kinetics and on the same sites as the LBR kinase , that are also phosphorylated in vivo . ^^^ |