Evolution of the mitochondrial genetic code III. Reassignment of CUN codons from leucine to threonine during evolution of yeast mitochondria |
| |
Authors: | Syozo Osawa David Collins Takeshi Ohama Thomas H Jukes Kimitsuna Watanabe |
| |
Institution: | (1) Laboratory of Molecular Biology, Nagoya University, 464 Nagoya, Japan;(2) Space Sciences Laboratory, University of California, 94720 Berkeley, California, USA;(3) Department of Life Chemistry, Tokyo Institute of Technology, Nagatsuta, 227 Yokohama, Japan |
| |
Abstract: | Summary Yeast mitochondria use UUR as the sole leucine codons. CUN, universal leucine codons, are read as threonine by aberrant threonine tRNA with anticodon sequence (UAG).The reassignment of CUN codons to threonine during yeast mitochondrial evolution could have proceeded by the disappearance of CUN codons from the reading frames of messenger RNA, through mutation mainly to UUR leucine codons as a result of AT pressure. We suggest that this was accompanied by a loss of leucine-accepting ability of tRNA Leu(UAG). This tRNA could have then acquired threonine-accepting activity through the appearance of an additional threonyl-tRNA synthetase. CUN codons that subsequently appeared from mutations of various other codons would have been translated as threonine. This change in the yeast mitochondrial genetic code is likely to have evolved through a series of nondisruptive nucleotide substitutions that produced no widespread replacement of leucine by threonine in proteins as a consequence. |
| |
Keywords: | Genetic code Codon reassignment (capture) CUN leucine codons CUN threonine codons tRNA Yeast mitochondria tRNA synthetases |
本文献已被 SpringerLink 等数据库收录! |
|