Translational coupling in a penP-lacZ gene fusion in Bacillus subtilis and Escherichia coli: use of AUA as a restart codon.

An out-of-frame fusion between the penicillinase gene (penP) of Bacillus licheniformis and the beta-galactosidase gene (lacZ) of Escherichia coli was shown to direct the synthesis of an active beta-galactosidase with the same electrophoretic mobility as the wild-type protein, both in B. subtilis and E. coli. This synthesis was dependent on translation of the truncated penP gene and appeared to result from translational coupling. The fusion point between penP and lacZ contained the sequence AUAG, in which the UAG and AUA codons were in-frame with the penP and lacZ reading units, respectively. N-terminal amino acid sequence analysis of the beta-galactosidase protein suggested that, both in B. subtilis and E. coli, reinitiation of translation occurred at the AUA codon present at the gene fusion point.