The DNA replication inhibitor microcin B17 is a forty‐three‐amino‐acid protein containing sixty percent glycine

Abstract

Microcin B17 is a low-molecular-weight protein that inhibits DNA replication in a number of enteric bacteria. It is produced by bacterial strains which harbor a 70-kilobase plasmid called pMccB17. Four plasmid genes (named mcbABCD) are required for its production. The product of the mcbA gene was identified by labelling minicells. The mcbA gene product was slightly larger when a mutation in any of the other three production genes was present. This indicates that these genes are involved in processing the primary mcbA product to yield the active molecule. The mcbA gene product predicted from the nucleotide sequence has 69 amino acids including 28 glycine residues. Microcin B17 was extracted from the cells by boiling in 100 mM acetic acid, 1 mM EDTA, and purified to homogeneity in a single step by high-performance liquid chromatography through a C18 column. The N-terminal amino acid sequence and amino acid composition demonstrated that mcbA is the structural gene for microcin B17. The active molecule is a processed product lacking the first 26 N-terminal residues. The 43 remaining residues include 26 glycines. While microcin B17 is an exported protein, the cleaved N-terminal peptide does not have the characteristic properties of a "signal sequence", which suggests that it is secreted by a mechanism different from that used by most secreted proteins of E. coli.

A signal peptide secretion-dependent bacteriocin from Carnobacterium divergens

“…Divergicin A contains six Gly-Gly paired residues in the mature peptide. The Gly-Gly motif is a feature of microcin B17, which is an inhibitor of DNA replication (7). The unique natures of the Ala-Ser-Ala processing site and the signal peptide indicate that divergicin A does not fit into established classes of bacteriocins.…”

The Highly Conserved TldD and TldE Proteins of Escherichia coli Are Involved in Microcin B17 Processing and in CcdA Degradation

“…Microcin B17 (MccB17) is a 3,093-Da peptide produced by Escherichia coli cells harboring an incFII plasmid called pMccB17 (13). It is active against most enterobacteria.…”

“…MccB17 production and immunity require seven open reading frames (mcbA, -B, -C, -D, -E, -F, and -G) organized in an operon located on the pMccB17 plasmid (19,45,46). The mcbA gene encodes premicrocin B17, the 69-amino-acid precursor of MccB17 (13). Premicrocin B17 is modified by the activity of the mcbB, -C, and -D gene products (MccB17 synthetase), yielding pro-MccB17 (32,55).…”

Nucleotide sequence of the Escherichia coli regulatory gene mprA and construction and characterization of mprA-deficient mutants

“…Microcin B17 (MccB17) is a bactericidal, glycine-rich peptide of about 3,200 Da which inhibits DNA replication in Escherichia coli by trapping a DNA gyrase-cleavable complex (4,15,31). The antibiotic is produced by E. coli strains containing a 5-kb DNA fragment from pMccB17 or other related plasmids (28,29).…”