期刊
MOLECULAR BIOLOGY AND EVOLUTION
卷 33, 期 11, 页码 2885-2889出版社
OXFORD UNIV PRESS
DOI: 10.1093/molbev/msw166
关键词
the genetic code; ciliates; translation termination; stop codon reassignment; alternative genetic decoding
资金
- Science Foundation Ireland [12/IA/1335, 13/1A/1853]
- National Institute of Health [GM061603]
- Science Foundation Ireland (SFI) [12/IA/1335] Funding Source: Science Foundation Ireland (SFI)
mRNA translation in many ciliates utilizes variant genetic codes where stop codons are reassigned to specify amino acids. To characterize the repertoire of ciliate genetic codes, we analyzed ciliate transcriptomes from marine environments. Using codon substitution frequencies in ciliate protein-coding genes and their orthologs, we inferred the genetic codes of 24 ciliate species. Nine did not match genetic code tables currently assigned by NCBI. Surprisingly, we identified a novel genetic code where all three standard stop codons (TAA, TAG, and TGA) specify amino acids in Condylostoma magnum. We provide evidence suggesting that the functions of these codons in C. magnum depend on their location within mRNA. They are decoded as amino acids at internal positions, but specify translation termination when in close proximity to an mRNA 30 end. The frequency of stop codons in protein coding sequences of closely related Climacostomum virens suggests that it may represent a transitory state.
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