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Mol Cell Biol, June 1998, p. 3201-3211, Vol. 18, No. 6
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

5' Processing of tRNA Precursors Can Be Modulated by the Human La Antigen Phosphoproteindagger

Hao Fan,1 John L. Goodier,1 Joel R. Chamberlain,2 David R. Engelke,2,3 and Richard J. Maraia1,*

Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892-2753,1 and Cellular and Molecular Biology Program2 and Department of Biological Chemistry,3 University of Michigan, Ann Arbor, Michigan 48109-0606

Received 24 November 1997/Returned for modification 18 January 1998/Accepted 6 March 1998

Eukaryotic precursor (pre)-tRNAs are processed at both ends prior to maturation. Pre-tRNAs and other nascent transcripts synthesized by RNA polymerase III are bound at their 3' ends at the sequence motif UUUOH [3' oligo(U)] by the La antigen, a conserved phosphoprotein whose role in RNA processing has been associated previously with 3'-end maturation only. We show that in addition to its role in tRNA 3'-end maturation, human La protein can also modulate 5' processing of pre-tRNAs. Both the La antigen's N-terminal RNA-binding domain and its C-terminal basic region are required for attenuation of pre-tRNA 5' processing. RNA binding and nuclease protection assays with a variety of pre-tRNA substrates and mutant La proteins indicate that 5' protection is a highly selective activity of La. This activity is dependent on 3' oligo(U) in the pre-tRNA for interaction with the N-terminal RNA binding domain of La and interaction of the C-terminal basic region of La with the 5' triphosphate end of nascent pre-tRNA. Phosphorylation of La is known to occur on serine 366, adjacent to the C-terminal basic region. We show that this modification interferes with the La antigen's ability to protect pre-tRNAiMet from 5' processing either by HeLa extract or purified RNase P but that it does not affect interaction with the 3' end of pre-tRNA. These findings provide the first evidence to indicate that tRNA 5'-end maturation may be regulated in eukaryotes. Implications of triphosphate recognition is discussed as is a role for La phosphoprotein in controlling transcriptional and posttranscriptional events in the biogenesis of polymerase III transcripts.

* Corresponding author. Mailing address: Building 6, Room 416, LMGR, NICHD, NIH, 9000 Rockville Pike, Bethesda, MD 20892-2753. Phone: (301) 402-3567. Fax: (301) 480-6863. E-mail: maraia{at}ncbi.nlm.nih.gov.

dagger R.J.M. dedicates this research paper to the memory of Christopher P. Cully.

Mol Cell Biol, June 1998, p. 3201-3211, Vol. 18, No. 6
0270-7306/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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