Article abstract
Nature Structural & Molecular Biology 16, 430 - 437 (2009)
Published online: 15 March 2009 | doi:10.1038/nsmb.1573
Precursor-product discrimination by La protein during tRNA metabolism
Mark A Bayfield1,3 & Richard J Maraia1,2
Abstract
La proteins bind pre-tRNAs at their UUU-3'OH ends, facilitating their maturation. Although the mechanism by which La binds pre-tRNA 3' trailers is known, the function of the RNA binding 
-sheet surface of the RNA-recognition motif (RRM1) is unknown. How La dissociates from UUU-3'OH–containing trailers after 3' processing is also unknown. Here we show that La preferentially binds pre-tRNAs over processed tRNAs or 3' trailer products through coupled use of two sites: one on the La motif and another on the RRM1 -surface that binds elsewhere on tRNA. Two sites provide stable pre-tRNA binding, whereas the processed tRNA and 3' trailer are released from their single sites relatively fast. RRM1 loop-3 mutations decrease affinity for pre-tRNA and tRNA, but not for the UUU-3'OH trailer, and impair tRNA maturation in vivo. We propose that RRM1 functions in activities that are more complex than UUU-3'OH binding. Accordingly, the RRM1 mutations also impair an RNA chaperone activity of La. The results suggest how La distinguishes precursor from product RNAs, allowing it to recycle onto a new pre-tRNA.
- Intramural Research Program, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA.
- Commissioned Corps, US Public Health Service, Bethesda, Maryland, USA.
- Present address: Department of Biology, York University, Toronto, ON, Canada.
Correspondence to: Richard J Maraia1,2 e-mail: maraiar@mail.nih.gov
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