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Nat Struct Mol Biol. 2006 Jul;13(7):611-8. Epub 2006 Jun 25.

Separate RNA-binding surfaces on the multifunctional La protein mediate distinguishable activities in tRNA maturation.

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Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, US National Institutes of Health, 31 Center Dr., Rm. 2A25, Bethesda, Maryland 20892, USA.


By sequence-specific binding to 3' UUU-OH, the La protein shields precursor (pre)-RNAs from 3' end digestion and is required to protect defective pre-transfer RNAs from decay. Although La is comprised of a La motif and an RNA-recognition motif (RRM), a recent structure indicates that the RRM beta-sheet surface is not involved in UUU-OH recognition, raising questions as to its function. Progressively defective suppressor tRNAs in Schizosaccharomyces pombe reveal differential sensitivities to La and Rrp6p, a 3' exonuclease component of pre-tRNA decay. 3' end protection is compromised by mutations to the La motif but not the RRM surface. The most defective pre-tRNAs require a second activity of La, in addition to 3' protection, that requires an intact RRM surface. The two activities of La in tRNA maturation map to its two conserved RNA-binding surfaces and suggest a modular model that has implications for its other ligands.

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