TOXICITY OF A HETEROLOGOUS LEUCYL-TRANSFER-RNA (ANTICODON CAG) IN THEPATHOGEN CANDIDA-ALBICANS - IN-VIVO EVIDENCE FOR NON STANDARD DECODING OF CUG CODONS

Plasmids containing derivatives of the Saccharomyces cerevisiae leucyl -tRNA (tRNA(3)(Leu)) gene that vary in anticodon sequence were constru cted and transformed into the pathogen Candida albicans and S. cerevis iae. C. albicans could readily be transformed with plasmids encoding l eucyl-tRNA genes with the anticodons CAA and UAA (recognizing the codo ns UUG and UUA) and expression of the heterologous tRNA(Leu) could be demonstrated by Northern RNA blotting. In contrast, no transformants w ere obtained if the anticodons were UAG (codons recognized CUN, UUR) a nd CAG (codon CUG), indicating that the insertion of leucine at CUG co dons is toxic for C. albicans. All tRNA(Leu)-encoding plasmids transfo rmed S. cerevisiae with equally high efficiencies. These results provi de in vivo evidence that non-standard decoding of CUG codons is essent ial for the viability of C. albicans.