Expression and characterization of HSPC129, a RNA polymerase II C-terminal domain phosphatase.

Phosphorylation status of RNA polymerase (RNAP) II's largest subunit C-terminal domain (CTD) plays an important role during transcription cycles. The reversible phosphorylation mainly occurs at serine 2 and serine 5 of CTD heptapeptide repeats and regulates RNAP II's activity during transcription initiation, elongation and RNA processing. Here we expressed and characterized HSPC129, a putative human protein bearing a CTD phosphatase domain (CPD). PCR analysis showed that it was ubiquitously expressed. HSPC129DeltaTM, the truncate HSPC129 with first 156 N terminal amino acids deleted, exhibited Mg(2+) dependent phosphatase activity at pH 5.0. Its specific CTD phosphatase activity was verified in vitro. Our research suggests that HSPC129 may regulate the dynamic phosphorylation of RNAP II CTD.