title: Molecular characterization of the largest subunit of Plasmodium falciparum RNA polymerase I.
abstract: Plasmodium species possess developmentally regulated ribosomal RNA (rRNA) genes. This report describes the expression and gene structure of the largest subunit of P. falciparum RNA polymerase I (RNAPI), which is responsible for the synthesis of rRNA. The RNAPI largest subunit gene was present as a single copy gene on chromosome 9. Three exons encode the 2910-amino acid RNAPI polypeptide (340 140 Da). A comparison of Plasmodium, Trypanosoma, and Saccharomyces cerevisiae nuclear RNAP largest subunits identified conserved amino acid positions and class-specific amino acid positions. Novel amino acid insertions were found between RNAPI conserved regions A and B (region A'), D and DE1 (region D'), DE2 and E (region DE2'), and F and G (region F'). Leucine zipper domains were found within regions D', DE2, and DE2'. A novel serine-rich repeat domain, a domain with homology to the C-terminal domain of eukaryotic upstream binding factor (UBF), and 4 highly conserved casein kinase II (CKII) Ser/Thr phosphorylation motifs were found within a 127-amino acid sub-region of enlarged region F'. The novel RNAPI serine-rich repeat contained a conserved motif, Ser-X3-Ser, which was also identified in the serine-rich repeat domains of the P. falciparum RNAPII and RNAPIII largest subunits, as well as within a highly homologous serine-rich repeat from trophozoite antigen R45. The results of this molecular analysis indicate that phosphorylation and dephosphorylation mechanisms regulate the activity of P. falciparum RNAPI.
authors.affiliation: Department of Microbiology, Dartmouth Medical School, Hanover, NH 03755-3842.
authors.forename: B A
authors.initials: BA
authors.lastname: Fox
authors.forename: W B
authors.initials: WB
authors.lastname: Li
authors.forename: M
authors.initials: M
authors.lastname: Tanaka
authors.forename: J
authors.initials: J
authors.lastname: Inselburg
authors.forename: D J
authors.initials: DJ
authors.lastname: Bzik
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D016054:DNA, Protozoan; D016521:Electrophoresis, Gel, Pulsed-Field; D005091:Exons; D006801:Humans; D007438:Introns; D008969:Molecular Sequence Data; D010963:Plasmodium falciparum / Q000201:enzymology*; D012318:RNA Polymerase I / Q000378:metabolism*; D015183:Restriction Mapping; D017386:Sequence Homology, Amino Acid
chemical_list: D016054:DNA, Protozoan; D012318:RNA Polymerase I