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, RepHI1A and RepHI1B, have been recently isolated and mapped on the R27 (IncHI1) genome (P. Gabant, P. Newnham, D. Taylor, and M. Couturier, J. Bacteriol. 175, 7697-7701, 1993). In the present work, the DNA sequence of RepHI1B was determined. It reveals DNA repeats of 17 base pairs located upstream and downstream from a gene coding for a 32 kilodalton protein (RepA) required for replication. Interestingly, RepA presents significant homology with other Rep proteins encoded by plasmids belonging to different incompatibility groups: P1 (IncY), Rts1 (IncT), RepFIB (IncFI) and RepHI1A (IncHI1). All these results provide strong evidence that the RepHI1B replicon of the IncHI1 subgroup belongs to the group of plasmids which control their copy number by an iteron mechanism.