Evolution of tRNAs and tRNA enes in Acholeplasma laidlawii

Abstract

The genes for 22 tRNA species from Acholeplasma laidlawil, belonging to the class Mollicutes (RAycoplasmas), have been cloned and sequenced. Sixteen genes are organized in 3 clusters consisting of eleven, three and two tRNA genes, respectively, and the other 6 genes exist as a single gene. The arrangement of tRNA genes in the 11-gene, the 3-gene and the 2-gene clusters reveals extensive similarity to several parts of the 21-tRNA or 16-tRNA gene cluster in Bacillus subtilis. The 11-gene cluster is also similar to the fRNA gene clusters found in other mycoplasma species, the 9-fRNA gene cluster In M.capricolum and in M.mycoides, and the 10-fRNA gene cluster in Spiroplasma mellferm. The results suggest that the tRNA genes in mycoplasmas have evolved from large tRNA gene clusters in the ancestral Gram-positive bacterial genome common to mycoplasmas and B.subtllls. The anticodon sequences including base modifications of 15 tRNA species from A.laidlawil were determined. The anticodon composition and codonrecognition patterns of A.laidlawli resemble those of Bacillus subtilis rather than those of ther mycoplasma species. © 1991 Oxford University Press.