FIG 1 .
Schematic map of the origin region of chromosome II (chrII) of V. cholerae and the effect of additional rctA on V. cholerae growth. (A) The region marked oriII is required in cis for initiation of replication, and the adjacent region marked incII is for controlling initiation. Initiation requires three trans-acting proteins, DnaA, IHF, and RctB. The binding sites for DnaA and IHF are shown by dark- and light-blue rectangles, respectively. The chrII-specific initiator, RctB, binds to two kinds of sites: the iterons (white arrowheads) and 39-mers (black rectangles). Iterons have built-in GATC sequences (red dots) that comprise the recognition site for the Dam methylase. Efficient binding of RctB to iterons requires the sites to be fully methylated. PrctB and PrctA are promoters responsible for transcribing rctB and rctA loci. The rctA locus is not translated. (B) A magnified view of the rctA locus, showing a parSII site for binding ParBII and three iteron-like sites within which also lies a 39-mer site. The sites were cloned under an inducible promoter, PBAD, to control transcription across them. The plots show the growth curves of wild-type cells (CVC209) with either the PBAD vector plasmid (CVC1111) or PBAD-rctA (CVC1142) or PBAD-RctB sites (CVC1143) or PBAD-parSII (CVC1144). The plot also includes generation times (τ) during the exponential growth phase of the cultures.