9.A.7 The Lactococcin 972 Immunity Protein (LactococcinIP) Family
A single sequenced protein comprises the lactococcin 972 family (1.C.37.1.1). This protein is plasmid-encoded in Lactococcus lactis. The mature protein is 66 aas long, but it is exported as a 91-residue precursor via the Sec (PSII) protein secretory pathway. It is cleaved extracellularly. It is encoded within a 2 cistron operon that also encodes a 563-residue immunity protein with 7 putative TMSs. Two transcripts are made: one encompasses the whole operon and is synthesized during the exponential growth phase; the other includes only the bacteriocin structural gene and is made both during the exponential and stationary growth phases. Distant homologues are found in other firmicutes.