Format

Send to

Choose Destination
Proc Natl Acad Sci U S A. 2015 Jun 2;112(22):6967-72. doi: 10.1073/pnas.1424909112. Epub 2015 May 18.

The messenger RNA decapping and recapping pathway in Trypanosoma.

Author information

1
Department of Infection Biology, Graduate School of Comprehensive Human Sciences and.
2
Departments of Biological Sciences.
3
the Human Biology Program, University of Tsukuba, Ibaraki 305-8575, Japan; and.
4
Department of Infection Biology, Graduate School of Comprehensive Human Sciences and Departments of Biological Sciences the Human Biology Program, University of Tsukuba, Ibaraki 305-8575, Japan; and Microbiology and Immunology, State University of New York, Buffalo, NY 14260 kiongho@md.tsukuba.ac.jp.

Abstract

The 5' terminus of trypanosome mRNA is protected by a hypermethylated cap 4 derived from spliced leader (SL) RNA. Trypanosoma brucei nuclear capping enzyme with cap guanylyltransferase and methyltransferase activities (TbCgm1) modifies the 5'-diphosphate RNA (ppRNA) end to generate an m7G SL RNA cap. Here we show that T. brucei cytoplasmic capping enzyme (TbCe1) is a bifunctional 5'-RNA kinase and guanylyltransferase that transfers a γ-phosphate from ATP to pRNA to form ppRNA, which is then capped by transfer of GMP from GTP to the RNA β-phosphate. A Walker A-box motif in the N-terminal domain is essential for the RNA kinase activity and is targeted preferentially to a SL RNA sequence with a 5'-terminal methylated nucleoside. Silencing of TbCe1 leads to accumulation of uncapped mRNAs, consistent with selective capping of mRNA that has undergone trans-splicing and decapping. We identify T. brucei mRNA decapping enzyme (TbDcp2) that cleaves m7GDP from capped RNA to generate pRNA, a substrate for TbCe1. TbDcp2 can also remove GDP from unmethylated capped RNA but is less active at a mature cap 4 end and thus may function in RNA cap quality surveillance. Our results establish the enzymology and relevant protein catalysts of a cytoplasmic recapping pathway that has broad implications for the functional reactivation of processed mRNA ends.

KEYWORDS:

RNA repair; Trypanosoma brucei; cap methylation; mRNA decapping; mRNA recapping

PMID:
26038549
PMCID:
PMC4460440
DOI:
10.1073/pnas.1424909112
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for HighWire Icon for PubMed Central
Loading ...
Support Center