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The biogenesis of transfer RNA is a process that requires many different factors. In this study, we describe a genetic screen aimed to identify gene products participating in this process. By screening for mutations lethal in combination with a sup61-T47: 2C allele, coding for a mutant form of, 10pt, legalpaperarticle amssymb amsfonts amsmath empty document \ (tRNA^Ser₂₆₀\) document, the nonessential TAN1 gene was identified. We show that the TAN1 gene product is required for formation of the modified nucleoside N 4 -acetylcytidine (ac 4 C) in tRNA. In Saccharomyces cerevisiae, ac 4 C is present at position 12 in tRNAs specific for leucine and serine as well as in 18S ribosomal RNA. Analysis of RNA isolated from a tan1 -null mutant revealed that ac 4 C was absent in tRNA, but not rRNA. Although no tRNA acetyltransferase activity by a GST-Tan1 fusion protein was detected, a gel-shift assay revealed that Tan1p binds tRNA, suggesting a direct role in synthesis of ac 4 C 12. The absence of the TAN1 gene in the sup61-T47: 2C mutant caused a decreased level of mature, 10pt, legalpaperarticle amssymb amsfonts amsmath empty document \ (tRNA^Ser₂₆₀\) document, indicating that ac 4 C 12 and/or Tan1p is important for tRNA stability.
Johansson et al. (Mon,) studied this question.