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Molecular and Cellular Biology, March 2009, p. 1202-1211, Vol. 29, No. 5
0270-7306/09/$08.00+0     doi:10.1128/MCB.01496-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Trypanosoma brucei Spliced Leader RNA Maturation by the Cap 1 2'-O-Ribose Methyltransferase and SLA1 H/ACA snoRNA Pseudouridine Synthase Complex {triangledown} ,{ddagger}

Jesse R. Zamudio,1,{dagger} Bidyottam Mittra,1 Arnab Chattopadhyay,2 James A. Wohlschlegel,2 Nancy R. Sturm,1* and David A. Campbell1

Department of Microbiology, Immunology & Molecular Genetics,1 Department of Biological Chemistry, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles, California 90095-14892

Received 24 September 2008/ Returned for modification 16 October 2008/ Accepted 10 December 2008

Kinetoplastid flagellates attach a 39-nucleotide spliced leader (SL) upstream of protein-coding regions in polycistronic RNA precursors through trans splicing. SL modifications include cap 2'-O-ribose methylation of the first four nucleotides and pseudouridine ({psi}) formation at uracil 28. In Trypanosoma brucei, TbMTr1 performs 2'-O-ribose methylation of the first transcribed nucleotide, or cap 1. We report the characterization of an SL RNA processing complex with TbMTr1 and the SLA1 H/ACA small nucleolar ribonucleoprotein (snoRNP) particle that guides SL {psi}28 formation. TbMTr1 is in a high-molecular-weight complex containing the four conserved core proteins of H/ACA snoRNPs, a kinetoplastid-specific protein designated methyltransferase-associated protein (TbMTAP), and the SLA1 snoRNA. TbMTAP-null lines are viable but have decreased SL RNA processing efficiency in cap methylation, 3'-end maturation, and {psi}28 formation. TbMTAP is required for association between TbMTr1 and the SLA1 snoRNP but does not affect U1 small nuclear RNA methylation. A complex methylation profile in the mRNA population of TbMTAP-null lines indicates an additional effect on cap 4 methylations. The TbMTr1 complex specializes the SLA1 H/ACA snoRNP for efficient processing of multiple modifications on the SL RNA substrate.

* Corresponding author. Mailing address: Department of Microbiology, Immunology, & Molecular Genetics, 4825 Molecular Sciences Building, 609 Charles E. Young Drive East, University of California at Los Angeles, Los Angeles, CA 90095-1489. Phone: (310) 206-5556. Fax: (310) 206-5231. E-mail: nsturm{at}ucla.edu

{triangledown} Published ahead of print on 22 December 2008.

{ddagger} Supplemental material for this article may be found at http://mcb.asm.org/.

{dagger} Present address: Koch Institute, Massachusetts Institute of Technology, Cambridge, MA 02139.

Molecular and Cellular Biology, March 2009, p. 1202-1211, Vol. 29, No. 5
0270-7306/09/$08.00+0     doi:10.1128/MCB.01496-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



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