Increased production of peptide deformylase eliminates retention of formylmethionine in bovine somatotropin overproduced in Escherichia coli.

In Escherichia coli and most other microorganisms, peptide synthesis is started at methionine start codons which are read only by N-formyl-methionine-tRNA. The formyl group is normally removed from the N-terminal Met residue of the peptide by peptide deformylase (PDF). However, it has been observed that overproduction of proteins in recombinant bacteria often yields protein products which are incompletely deformylated. Certain proteins could be poor substrates for PDF and exhibit incomplete deformylation, particularly when they are overproduced. Strains of E. coli which overproduce bovine somatotropin (BST) have a significant fraction of the BST with the formyl group retained. The PDF gene was isolated and positioned into a BST production vector in such a way that the BST and PDF genes were coexpressed. In strains containing this coexpression vector, the levels of PDF were increased and formylated BST was undetectable.