Effect of B. subtilis TRNA(Trp) on readthrough rate at an opal UGA codon.

Bacillus subtilis has been thought to have a high readthrough rate at the UGA stop codon because no opal suppressor tRNA has been isolated so far [Lovett et al. (1991) J. Bacteriol. 173, 1810-1812]. To examine whether a tRNATrp which we have characterized [Matsugi et al. (1992) Nucleic Acids Res. 20, 3514] has the ability to read the UGA codon, in vitro translation was performed with a synthetic mRNA containing a test codon, UGA, UAG, UAA, or UGG, in a reading frame. Addition of Trp-tRNATrp to the system significantly increased the readthrough rate only in the case of UGA. This suggests that this tRNATrp has a dual recognition pattern in B. subtilis, i.e., for the canonical tryptophan codon and for readthrough at the UGA stop codon.