Carboxy terminal domain of largest subunit of RNA polymerase II of Leishmania donovani has unusually low number of phosphorylation sites

Abstract

Background: The C-terminal domain (CTD) of the largest subunit of RNA polymerase II in higher eukaryotes has an altered form in Leishmania donovani. To determine whether this is a general feature of the kinetoplastida and to investigate the role of this domain in parasitic RNA pol II transcription, we isolated the gene encoding RNA pol II LS (rpolIILS) and analyzed its C-terminal domain. The discreteness observed may be due to a functional constraint delineating parasite from host. Material/Methods: The gene for L. donovani rpolIILS was picked up and sequenced. The CTD of L. donovani rpolIILS was purified as a His-tagged recombinant protein and phosphorylated with a crude kinase extract from L. donovani. An immunoblot analysis of the phosphorylated CTD and photo-crosslinked L. donovani nuclear extracts was done using anti-CTD antibody. Results: The L. donovani rpolIILS is encoded by a single-copy gene. Its transcript is matured postranscriptionally, with the mini-exon trans-spliced 397 bases upstream of the initiation site. The uniqueness of Leishmania rpolIILS CTD according to prediction analysis was corroborated with in vitro phosphorylation of the recombinant protein. Photoaffinity labelling of L. donovani nuclear run-on transcripts and immunoblot analysis using anti-CTD antibody could identify the active form of RNA polymerase II enzyme in this parasite. Conclusions: The L. donovani rpolIILS possesses a unique C-terminal extension lacking the characteristic repeats but containing serine residues as a potential phosphorylation site. Anti-CTD antibody could recognize a single molecular species for the RNA pol II enzyme in L. donovani.