Dja. Netz et al., Molecular characterisation of aureocin A70, a multipeptide bacteriocin isolated from Staphylococcus aureus, J MOL BIOL, 311(5), 2001, pp. 939-949
Staphylococcus aureus A70 produces a heat-stable bacteriocin designated aur
eocin A70. Aureocin A70 is encoded within a mobilisable 8 kb plasmid, pRJ6,
and is active against Listeria monocytogenes. Experiments of transposition
mutagenesis and gene cloning had shown that aureocin A70 production and im
munity were associated with the HindIII-A and B fragments of pRJ6. Therefor
e, a 6332 bp region of the plasmid, encompassing both these fragments, was
sequenced using a concatenation DNA sequencing procedure. DNA sequence and
genetic analyses revealed the presence of three transcriptional units that
appear to be involved in bacteriocin activity. The first transcriptional un
it contains a single gene, aurT, which encodes a protein that resembles an
ATP-dependent transporter, similar to those involved in lantibiotic export.
AurT is required for aureocin A70 production and it appears to be essentia
l for mobilisation of pRJ6. The second putative operon contains two open re
ading frames (ORFs); the first gene, orfA, is predicted to encode a protein
similar to small repressor proteins found in some Archaea, whose function
remains to be elucidated. The second gene, orfB, codes for an 138 amino aci
d residue protein which shares a number of characteristics (high pI and hyd
rophobicity profile) with proteins associated with immunity, needed for sel
f-protection against bacteriocin. Four other genes are present in the third
operon, aurABCD. aurABCD encode four related peptides that are small (30-3
1 amino acid residues), strongly cationic (pI of 9.85 to 10.04) and highly
hydrophobic. Theses peptides also have a high content of small amino acid r
esidues like glycine and alanine, and no cysteine residue. Tn917-lac insert
ional mutations, which affected aureocin A70 activity, reside within operon
aurABCD. Analysis of purified bacteriocin preparations by mass spectrometr
y demonstrated that all four peptides encoded by aurABCD operon are produce
d, expressed and excreted without post-translational modifications. Thus, a
ureocin A70 is a multi-peptide non-lantibiotic bacteriocin, which is transp
orted without processing. (C) 2001 Academic Press.