Length and structural effect of signal peptides derived fromBacillus subtilisα-amylase on secretion ofEscherichja coliβ-lactamase in B.subtiliscells

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Abstract
The precursor of Bacillus subtilis α-amylase contains an NH extension of 41 amino acid residues as the signal sequence. The E. coli β-lactamase structural gene was fused with the DNA for the promoter and signal sequence regions. Activity of β-lactamase was expressed and more than 95% of the activity was secreted into the culture medium. DNA fragments coding for short signal sequences 28, 31, and 33 amino acids from the initiator Met were prepared and fused with the β-lactamase structural gene. The sequences of 31 and 33 amino acid residues with Ala COOH-terminal amino acid were able to secrete active β-lactamase from B. subtilis cells. However β-lactamase was not secreted into the culture medium by the shorter signal sequence of 28 amino acid residues, which was not cleaved. Molecular weight analysis of the extracellular and cell-bound β-lactamase suggested that the signal peptide of B. subtilis α-amylase was the first 31 amino acids from the initiator Met. The significance of these results was discussed in relation to the predicted secondary structure of the signal sequences.