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i6A-deficient tRNA from an Antisuppressor Mutant of Saccharomyces cerevisiae
Abstract
Our goal was to screen for strains of the yeast Saccharomyces cerevisiae with mutations in genes for tRNA modifying enzymes. The genetic screening for these mutants was based on the probable correlation between loss of base modification and reduction in the efficiency of suppression of a UAA nonsense suppressing tRNA. The existence of such a correlation was suggested by early in vitro findings (Gefter and Russell 1969) and has since been supported by recent in vivo studies (Colby et al. 1976; Marinus et al. 1975).
We have isolated a mutant that contains 1.5% of the normal tRNA complement of i6A (isopentenyladenosine). This mutant affords the opportunity to compare in vitro results with in vivo observations. The mutation, which has been designated mod5-1, reduces the suppression by a dominant UAA suppressor, SUP7-1 (Gilmore 1967), so that only the more easily suppressed of several UAA mutations are suppressed. SUP7-1 is one of several efficient tyrosine-inserting UAA suppressors and most probably codes for an altered tRNATyr (Gilmore et al. 1971;...
DOI: http://dx.doi.org/10.1101/0.395-406