A Mutation in a Methionine tRNA Gene Suppresses the prp2-1 Ts Mutation and Causes a Pre-mRNA Splicing Defect in Saccharomyces cerevisiae

Corresponding author: Ren-Jang Lin, Department of Molecular Biology, Beckman Research Institute of the City of Hope, 1450 E. Duarte Rd., Duarte, CA 91010-3011., rlin{at}coh.org (E-mail)

Communicating editor: S. SANDMEYER

The PRP2 gene in Saccharomyces cerevisiae encodes an RNA-dependent ATPase that activates spliceosomes for the first transesterification reaction in pre-mRNA splicing. We have identified a mutation in the elongation methionine tRNA gene EMT1 as a dominant, allele-specific suppressor of the temperature-sensitive prp2-1 mutation. The EMT1-201 mutant suppressed prp2-1 by relieving the splicing block at high temperature. Furthermore, EMT1-201 single mutant cells displayed pre-mRNA splicing and cold-sensitive growth defects at 18°. The mutation in EMT1-201 is located in the anticodon, changing CAT to CAG, which presumably allowed EMT1-201 suppressor tRNA to recognize CUG leucine codons instead of AUG methionine codons. Interestingly, the prp2-1 allele contains a point mutation that changes glycine to aspartate, indicating that EMT1-201 does not act by classical missense suppression. Extra copies of the tRNA^Leu(UAG) gene rescued the cold sensitivity and in vitro splicing defect of EMT1-201. This study provides the first example in which a mutation in a tRNA gene confers a pre-mRNA processing (prp) phenotype.

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