Structurally conserved and functionally divergent yeast Ssu72 phosphatases

The eukaryotic Ssu72 factor is involved in several RNA biogenesis processes. It has phosphatase activity on the carboxy-terminal domain (CTD) of the major subunit of RNA polymerase II. The Kluyveromyces lactis Ssu72 (KlSsu72) shows in vitro phosphatase activity for the pNPP substrate, and this activity is inhibited by ortho-vanadate. The expression of KlSsu72 in Saccharomyces cerevisiae shows defective CTD serine5-P phosphatase activity and reveals the importance of Ssu72 for the normal CTD serine5-P levels at two growth states. The divergence is emphasised by the remarkable changes in RNA14 alternative 3′-end RNA processing, which are independent of the CTD serine5-P levels.