Binding sites of integration host factor in oriT of plasmid R100.

Plasmid R100 confers conjugal transfer ability on its host bacteria and is transmitted from one host to another.R 100 and several other conjugative plasmids, such as F and R 1, share structural and functional homology in the tra region which is responsible for DNA transfer (7,8,23,27).The tra region contains at least 26 genes which are considered to be organized into three main operons, traM, traJ and tra Y I(Z) (for recent reviews, see references 18, 36).However, several chromosomal mutations are also known to influence genetic transfer (for a review, see reference 28).For example, transfer of R 100 and F is reduced in a host mutant lacking IHF (integration host factor) (3,10).There are possible IHF recognition sequences in the region containing the origin of transfer, oriT, of R100 (20; see Fig. 1B), but any of these sequences are not actually shown to be bound by IHF.Here we report the determination of the location of the two IHF binding sites in oriT.One site (designated ihfA) was located between the proposed nicking sites and the TraY protein binding site sbyA.The other (designated ihfB) was upstream of the