1983 Volume 32 Issue 12 Pages 609-616
An Escherichia coli strain, CR34, harboring both pSC101 and ColEl-amp plasmids was exposed to media containing rifampicin (100μg/ml) and/or chloramphenicol (180 μg/ml) and the cells were labeled for 20 min with 3H-thymine at 3, 25 and 50 min after exposure to drug (s) . The plasmid DNA synthesis was assayed by DNA-DNA hybridization with 14C-labeled pSC 134 DNA as internal marker. In the presence of rifampicin, the replication of pSC 101 was from 57 to 104% that in its absence, and that of ColEl-amp was from 17 to 26%. The DNA replication of pSC 101 after addition of chloramphenicol was reduced to 35 to 75%, and that of ColEl-amp was reduced to 39% and then restored to 92%. This restoration was not observed in the presence of rifampicin.