Origin-specific reduction of ColE1 plasmid copy number due to mutations in a distinct region of the Escherichia coli RNA polymerase

• DOI: 10.1007/s00438-002-0689-y
• Publication Date: 2003-02-13T05:27:25Z
• Authors: J. Ederth; L. Isaksson; F. Abdulkarim
• Keywords: 0303 health sciences; Blotting, Western; DNA-Directed RNA Polymerases; 3. Good health; 03 medical and health sciences; Amino Acid Substitution; Mutation; Escherichia coli; Promoter Regions, Genetic; N-Glycosyl Hydrolases; Ribosomes; Plasmids; Sequence Deletion

Mutations affecting a region of the Escherichia coli RNA polymerase have been isolated that specifically reduce the copy number of ColE1-type plasmids. The mutations, which result in a single amino acid alteration (G1161R) or a 41-amino acid deletion (Delta1149-1190) are located near the 3'-terminal region in the rpoC gene, which encodes the largest subunit (beta ') of the RNA polymerase. The rpoC deletion and the point mutation cause over 20- and 10-fold reductions, respectively, in the copy number of ColE1. ColE1 plasmid numbers are regulated by two plasmid-encoded RNAs: RNA II, which acts as a preprimer for the DNA polymerase I to start initiation of replication, and RNA I, its antisense inhibitor. Altered expression from the RNA I and RNA II promoters in vivo was observed in the RNA polymerase mutants. The RNA I/RNA II ratio is higher in the mutants than in the wild-type strain and this is most probably the main reason for the reduction in the ColE1 copy number in the two rpoC mutants.