HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: rna.2250606v1 12/3/488    most recent Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by HALL, M. P. Articles by HO, C. K. Search for Related Content PubMed PubMed Citation Articles by HALL, M. P. Articles by HO, C. K. Social Bookmarking                   What's this?

Characterization of a Trypanosoma brucei RNA cap (guanine N-7) methyltransferase

Department of Biological Sciences, State University of New York at Buffalo, Buffalo, New York 14260, USA

Reprint requests to: C. Kiong Ho, Department of Biological Sciences, State University of New York at Buffalo, Buffalo, NY 14260, USA; e-mail: kiongho{at}buffalo.edu; fax: (212) 717-3623.

The m⁷GpppN cap structure of eukaryotic mRNA is formed by the sequential action of RNA triphosphatase, guanylyltransferase, and (guanine N-7) methyltransferase. In trypanosomatid protozoa, the m⁷GpppN is further modified by seven methylation steps within the first four transcribed nucleosides to form the cap 4 structure. The RNA triphosphatase and guanylyltransferase components have been characterized in Trypanosoma brucei. Here we describe the identification and characterization of a T. brucei (guanine N-7) methyltransferase (TbCmt1). Sequence alignment of the 324–amino acid TbCmt1 with the corresponding enzymes from human (Hcm1), fungal (Abd1), and microsporidian (Ecm1) revealed the presence of conserved residues known to be essential for methyltransferase activity. Purified recombinant TbCmt1 catalyzes the transfer of a methyl group from S-adenosylmethionine to the N-7 position of the cap guanine in GpppN-terminated RNA to form the m⁷GpppN cap. TbCmt1 also methylates GpppG and GpppA but not GTP or dGTP. Mutational analysis of individual residues of TbCmt1 that were predicted—on the basis of the crystal structure of Ecm1—to be located at or near the active site identified six conserved residues in the putative AdoMet- or cap-binding pocket that caused significant reductions in TbCmt1 methyltransferase activity. We also report the identification of a second T. brucei RNA (guanine N-7) cap methyltransferase (named TbCgm1). The 1050–amino acid TbCgm1 consists of a C-terminal (guanine N-7) methyltransferase domain, which is homologous with TbCmt1, and an N-terminal guanylyltransferase domain, which contains signature motifs found in the nucleotidyl transferase superfamily.

Keywords: mRNA capping; m⁷G methyltransferase; Trypanosoma brucei

CiteULike    Connotea    Del.icio.us    Digg    Reddit    Technorati    What's this?

This article has been cited by other articles:

				M. P. Hall and C. K. Ho Functional characterization of a 48 kDa Trypanosoma brucei cap 2 RNA methyltransferase Nucleic Acids Res., November 14, 2006; 34(19): 5594 - 5602. [Abstract] [Full Text] [PDF]