A NORMAL TRNA(ARG) COMPLEMENTS THE RAD18X MUTATION IN SCHIZOSACCHAROMYCES-POMBE

A clone that complements the rad18x mutation of Schizosaccharomyces po mbe has been isolated from the screening of yeast genomic DNA library. This clone with a 4.6 kb DNA insert was named pPS1 and appeared to pa rtially complement the UV and methyl methanesulfonate (MMS) sensitivit y of rad18 mutatant The region responsible for the complementing activ ity on rad18x mutation was located within a 1.0 kb BamHI-SmaI fragment within the pPS1. Northern blot and nucleotide sequence analyses of th is fragment revealed that the DNA insert of pPS1 carries a normal tRNA gene consisting of 73 base pairs without an intron. Its anticodon seq uence is ACG which primarily decodes CGT (arginine). A possible RNA po lymerase III termination site is present downstream from the end of th e tRNA. The KJ3 strain of S. pombe which has a known amber (UAG) mutat ion was suppressed by the transformation with pPS1. These results sugg est that a normal tRNA(Arg) in 1.0 kb BamHI-SmaI fragment of pPS1 coul d overcome the nonsense mutation in the rad18 mutant when it is expres sed in a sufficient quantity.