Seryl-tRNA synthetase is not responsible for the evolution of CUG codon reassignment in Candida albicans.
A number of Candida species translate the standard leucine-CUG codon as serine using a novel ser-tRNA(CAG). This tRNA, which has an unusual anticodon stem-loop structure, has been implicated in the evolution of this codon reassignment. However, such a sense codon reassignment might also require a change in the specificity of the cognate aminoacyl tRNA-synthetase, in this case the ser-tRNA synthetase. Here we describe the cloning and sequence analysis of the C. albicans seryl aminoacyl-tRNA synthetase (CaSerRS) gene (CaSES1). The predicted CaSerRS sequence shows a significant level of amino acid identity to SerRs from other organisms and fully complements a S. cerevisiae SerRS null strain without any apparent defect in growth rate. This suggests that the SerRS recognizes and charges S. cerevisiae ser-tRNAs with similar efficiency to that of the S. cerevisiae SerRS. Using an antibody raised against CaSerRS, we also demonstrate the presence of SerRS in a range of Candida spp. showing CUG codon reassignment. We conclude that the key element in CUG reassigment in Candida spp. is the tRNA that decodes the CUG codon rather than a SerRS structural change. The nucleotide sequence of the CaSES1 gene has been deposited at GenBank under Accession No. AF290915.
Department of Biosciences, University of Kent, Canterbury, Kent CT2 7NJ, UK.
J M
JM
O'Sullivan
M J
MJ
Mihr
M A
MA
Santos
M F
MF
Tuite
D000595:Amino Acid Sequence; D002176:Candida albicans / Q000235:genetics*; D003001:Cloning, Molecular; D019143:Evolution, Molecular; D015870:Gene Expression; D005815:Genetic Code; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D014176:Protein Biosynthesis / Q000235:genetics*; D012343:RNA, Transfer / Q000235:genetics; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D012694:Serine / Q000235:genetics*; D012714:Serine-tRNA Ligase / Q000235:genetics* / Q000378:metabolism
D012694:Serine; D012343:RNA, Transfer; D012714:Serine-tRNA Ligase