Abstract
Bacillus brevis 47 secretes vast amounts of proteins derived from both middle wall protein (MWP) and outer wall protein into the medium. The 5' region of the cell wall protein gene operon was cloned into Bacillus subtilis and subsequently into B. brevis 47. On the basis of the nucleotide sequence analysis, an open reading frame coding for MWP was identified on the cloned DNA fragment. Two potential translation initiation sites for the MWP gene are located tandemly in the same reading frame. Each of the sites contains a sequence highly homologous to the 3' end of B. brevis rRNA and an initiation codon. The translational fusion of the 5' region of the MWP gene with the Bacillus licheniformis alpha-amylase gene resulted in the efficient expression of the alpha-amylase gene in B. brevis 47. Of the two potential translation initiation sites, the one located upstream could be eliminated without affecting the expression of the MWP-alpha-amylase fusion gene, suggesting that MWP is synthesized in a precursor form with a signal peptide of 23 amino acid residues. S1 nuclease mapping of the cell wall protein gene transcripts suggested the possibility of the existence of several promoters in the 5' region within 300 base pairs from the translation initiation sites; one promoter was definitely localized within this part of the 5' region, and it was capable of expressing a heterologous gene fusion at a high level. The roles of the apparent structural complexity of the 5' region of the cell wall protein gene operon are discussed in connection with the efficient gene expression.