Trans‐translation mediated by Bacillus subtilis tmRNA

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Abstract
Trans‐translation, in which a ribosome switches between translation of an mRNA and a tmRNA, produces a chimera polypeptide of an N‐terminal truncated polypeptide and a C‐terminal tag‐peptide encoded by tmRNA. One of the tmRNA binding proteins, a ribosomal protein S1, has not been found in a group of Gram‐positive bacteria. In this study, the trans‐translation reaction with tmRNA from Bacillus subtilis belonging to this group was examined. When a truncated gene lacking a termination codon was expressed in B. subtilis, a 15‐amino acid tag‐peptide derived from tmRNA was identified in the C‐termini of the trans‐translation products. An identical tag‐peptide was also found at the C‐termini of the products from a truncated gene, when it was coexpressed with B. subtilis tmRNA in Escherichia coli. B. subtilis tmRNA was functional, although much less efficiently, in the in vitro poly(U)‐dependent tag‐peptide synthesis system of E. coli. A comparison of two bacterial tmRNAs suggests that the rule for determining the tag‐initiation point on tmRNA may be the same in Gram‐positive and Gram‐negative bacteria.