REPLICATION OF MINICHROMOSOMES IN A HOST IN WHICH CHROMOSOME-REPLICATION IS RANDOM

Minichromosomes are plasmids with the origin of chromosome replication , oriC, as their only origin of replication. In Escherichia coli, mini chromosomes are compatible with the chromosome and replicate in a cell -cycle-specific manner at the same time as oriC located on the chromos ome initiates replication. In int strains, oriC has been inactivated a nd replaced by a plasmid origin. Because plasmids control their own re plication, chromosome replication is uncoupled from the normal cell-cy cle control and is random with respect to the cell cycle in the int st rains. We have used an intP1 strain to address the question of whether minicromosome replication is coupled to the replication of the chromo some or is governed by cell-cycle-specific signals. Minichromosome rep lication was analysed by density-shift experiments and found not to be random in the randomly replicating intP1 host. This suggests that the cell-cycle-specific control functions of oriC replication are operati ng also in the intP1 strain.