NUCLEOTIDE-SEQUENCE AND REPLICATION CHARACTERISTICS OF REPHI1B - A REPLICON SPECIFIC TO THE INCHI1 PLASMIDS

The IncHI1 plasmids are multireplicon plasmids. They contain at least three autoreplicative regions, one of which is closely related to the RepFIA replicon of F. Two other IncHI1-specific replicons, RepHI1 A an d RepHI1B, have been recently isolated and mapped on the R27 (In-cHI1) genome (P. Gabant, P. Newnham, D. Taylor, and M. Couturier, J Bacteri ol. 175, 7697-7701, 1993). In the present work, the DNA sequence of Re pHI1 B was determined. It reveals DNA repeats of 17 base pairs located upstream and downstream from a gene coding for a 32 kilodalton protei n (RepA) required for replication. Interestingly, RepA presents signif icant homology with other Rep proteins encoded by plasmids belonging t o different incompatibility groups: P1 (IncY), Rts1 (IncT), RepFIB (In cFI) and RepHI1A (IncHI1). All these results provide strong evidence t hat the RepHI1B replicon of the IncHI1 subgroup belongs to the group o f plasmids which control their copy number by an iteron mechanism. (C) 1994 Academic Press, Inc.