Summary: To study the effect of inserted peptides on the secretion and processing of exported proteins in and , pBR322-derived DNA fragments coding for small peptides were inserted between the DNA coding for the 31 amino acid α-amylase signal peptide and that coding for the mature part of the extracellular thermostable α-amylase of . Most of the inserted peptides (21 to 65 amino acids) decreased the production of the enzyme in and , the effect of each peptide being similar in the two strains. In contrast, with one peptide (a 21 amino acid sequence encoded by the extra DNA in pTUBE638), the production of α-amylase was enhanced more than 1·7-fold in in comparison with that of the parent strain. The molecular masses of the thermostable α-amylases in the periplasm of the transformants varied for each peptide insert, whereas those in the culture supernatants of the transformants had molecular masses similar to that of the mature enzyme. Based on the NH-terminal amino acid sequence of the hybrid protein from pTUBE638, it was shown that in , the NH-terminally extended thermostable α-amylase was translocated and remained in the periplasm after the 31 amino acid signal sequence was removed. In the case of , after the removal of a 34-amino acid signal sequence, the hybrid protein was secreted and processed to the mature form.


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