Molecular gentic analysis of the trfB and korB region of broad host range plasmid RK2

Abstract

A 3.2 kb region of the broad host range IncP plasmid RK2 (indistinguishable from RP1, RP4, R68 and R18) anticlockwise from the EcoRI site may be separated phenotypically into three loci. The trfB/korA/korD locus both complements a temperature-sensitive maintenance mutation and suppresses the deleterious effects of the loci kilA and kilD; the incC locus expresses incompatibility towards complete RK2-like replicons, and the korB locus suppresses the host lethal effect the kilB locus. Transcriptional fusions of the galK gene to various segments of this region revealed that all three loci are transcribed anticlockwise from a common promoter. A weak secondary promoter may also contribute to the expression of korB. Analysis of the sizes of the polypeptides produced from these segments led to the identification of two cistrons, the first encoding a polypeptide of 38 kDal associated with incC function and the second a polypeptide of 49 kDal associated with korB activity. The trfB/korA/korD activities are associated with a polypeptide of 14kDal which may be an N-terminal fragment of the incC-associated polypeptide.