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Molecular and Cellular Biology, November 2003, p. 7909-7919, Vol. 23, No. 21
0270-7306/03/$08.00+0     DOI: 10.1128/MCB.23.21.7909-7919.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Trypanosoma brucei RNA Editing Complex

Band II Is Structurally Critical and Maintains Band V Ligase, Which Is Nonessential

Sean F. O'Hearn, Catherine E. Huang,{dagger} Mike Hemann,{ddagger} Alevtina Zhelonkina, and Barbara Sollner-Webb*

Department of Biological Chemistry, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205

Received 18 April 2003/ Returned for modification 23 May 2003/ Accepted 29 July 2003

Maturation of Trypanosoma brucei mitochondrial mRNA involves massive posttranscriptional insertion and deletion of uridine residues. This RNA editing utilizes an enzymatic complex with seven major proteins, band I through band VII. We here use RNA interference (RNAi) to examine the band II and band V proteins. Band II is found essential for viability; it is needed to maintain the normal structure of the editing complex and to retain the band V ligase protein. Previously, band III was found essential for certain activities, including maintenance of the editing complex and retention of the band IV ligase protein. Thus, band II and band V form a protein pair with features analogous to the band III/band IV ligase pair. Since band V is specific for U insertion and since band IV is needed for U deletion, their parallel organization suggests that the editing complex has a pseudosymmetry. However, unlike the essential band IV ligase, RNAi to band V has only a morphological but no growth rate effect, suggesting that it is stimulatory but nonessential. Indeed, in vitro analysis of band V RNAi cell extract demonstrates that band IV can seal U insertion when band V is lacking. Thus, band IV ligase is the first activity of the basic editing complex shown able to serve in both forms of editing. Our studies also indicate that the U insertional portion may be less central in the editing complex than the corresponding U deletional portion.

* Corresponding author. Mailing address: Department of Biological Chemistry, Johns Hopkins University School of Medicine, 725 N. Wolfe St., Baltimore, MD 21205-2185. Phone: (410) 955-6278. Fax: (410) 955-0192. E-mail: bsw{at}jhmi.edu.

{dagger} Present address: Carnegie Institute, Department of Embryology, Baltimore, MD 21210.

{ddagger} Present address: Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724.

Molecular and Cellular Biology, November 2003, p. 7909-7919, Vol. 23, No. 21
0022-538X/03/$08.00+0     DOI: 10.1128/MCB.23.21.7909-7919.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.



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