Penicillin acylase fromE. coli: unique gene-protein relation

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Abstract
The nucleotide sequence of the gene (pac) coding for penicillin G acylase from E. coli ATCC 11105 was determined and correlated with the primary structure of the two constituent subunits of this enzyme. The pac gene open reading frame consists of four structural domains: (i) Nucleotide positions 1–78 coding for a signal peptide, (ii) positions 79–705 coding for the a subunit, (iii) positions 706–867 coding for a spacer peptide, and (iv) positions 868–2538 coding for the B subunit. Plasmids were constructed which direct the synthesis of a pac gene product lacking the signal peptide, and the synthesis of the a subunit or the B subunit. The following results were obtained: (i) The two dissimilar subunits are processing products of a single precursor poly-peptide; the spacer peptide is removed during processing; (ii) the precursor polypeptide lacking the signal sequence is accumulated in the cytoplasm; it is not processed proteolyti-cally in the cytoplasm and it does not display enzyme activity. Processing, therefore, requires translocation through the cytoplasmic membrane; (iii) processing follows a distinct sequential pathway in vitro.