(A) GST-SRPK1 was incubated with 0, 150, 250 and 350 mM DTT at room temperature for 14 h, then analyzed on 10% SDS-PAGE under reducing conditions and stained with Coomassie Blue. No degradation of GST-SRPK1 was observed following its overnight incubation with DTT. (B) GST-SRPK1 was incubated with 0, 150, 250 and 350 mM DTT at room temperature for 2, 5 and 14 h respectively and then used in kinase assays with GST-LBRNT(62–92) as substrate. Phosphorylated proteins were separated by 12% SDS-PAGE, stained with Coomassie Blue and autoradiographed. Only the relevant part of the autorad corresponding to phosphorylated GST-LBRNt(62–92) is shown. (C) Signals were quantified by excising the radioactive bands from the gel and scintillation counting. Measurements were done in triplicate. Error bars designate standard error.