rctB mutations that increase copy number of Vibrio cholerae oriCII in Escherichia coli

► We isolated mutations in the Vibrio cholerae chromosome II replication initiation protein RctB. ► All mutations gave a copy-up phenotype in a minichromosome based system in Escherichia coli. ► All mutations decreased the RctB-RctB interaction. ► All mutations influenced rctB autoregulation. ► The maximal C-terminal deletion giving a functional RctB was165 amino acids.