From in vitro translation studies we have previously demonstrated the existence of an apparent efficient UAG (amber) suppressor tRNA in the dimorphic fungus Candida albicans (Santos et al., 1990). Using an in vitro assay for termination codon readthrough the tRNA responsible was purified to homogeneity from C.albicans cells. The determined sequence of the purified tRNA predicts a 5'-CAG-3' anticodon that should decode the leucine codon CUG and not the UAG termination codon as originally hypothesized. However, the tRNA(CAG) sequence shows greater nucleotide homology with seryl-tRNAs from the closely related yeast Saccharomyces cerevisiae than with leucyl-tRNAs from the same species. In vitro tRNA-charging studies demonstrated that the purified tRNA(CAG) is charged with Ser. The gene encoding the tRNA was cloned from C.albicans by a PCR-based strategy and DNA sequence analysis confirmed both the structure of the tRNA(CAG) and the absence of any introns in the tRNA gene. The copy number of the tRNA(CAG) gene (1-2 genes per haploid genome) is in agreement with the relatively low abundance (