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Molecular and Cellular Biology, July 2002, p. 4652-4660, Vol. 22, No. 13
0270-7306/02/$04.00+0     DOI: 10.1128/MCB.22.13.4652-4660.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Distinct Functions of Two RNA Ligases in Active Trypanosoma brucei RNA Editing Complexes

Jorge Cruz-Reyes,,{dagger} Alevtina G. Zhelonkina, Catherine E. Huang, and Barbara Sollner-Webb*

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

Received 1 February 2002/ Returned for modification 13 March 2002/ Accepted 28 March 2002

Trypanosome RNA editing is a unique U insertion and U deletion process that involves cycles of pre-mRNA cleavage, terminal U addition or U removal, and religation. This editing can occur at massive levels and is directed by base pairing of trans-acting guide RNAs. Both U insertion and U deletion cycles are catalyzed by a single protein complex that contains only seven major proteins, band I through band VII. However, little is known about their catalytic functions, except that band IV and band V are RNA ligases and genetic analysis indicates that the former is important in U deletion. Here we establish biochemical approaches to distinguish the individual roles of these ligases, based on their distinctive ATP and pyrophosphate utilization. These in vitro analyses revealed that both ligases serve in RNA editing. Band V is the RNA editing ligase that functions very selectively to seal in U insertion (IREL), while band IV is the RNA editing ligase needed to seal in U deletion (DREL). In combination with our earlier findings about the cleavage and the U-addition/U-removal steps of U deletion and U insertion, these results show that all three steps of these editing pathways exhibit major differences and suggest that the editing complex could have physically separate regions for U deletion and U insertion.

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

{dagger} Present address: Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843.

Molecular and Cellular Biology, July 2002, p. 4652-4660, Vol. 22, No. 13
0022-538X/02/$04.00+0     DOI: 10.1128/MCB.22.13.4652-4660.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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