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J. Bacteriol., Jan 1998, 265-273, Vol 180, No. 2
M Bipatnath, PP Dennis and H Bremer
The macromolecular composition and a number of parameters affecting
chromosome replication were examined over a range of exponential growth
rates in two common Escherichia coli strains, B/r and K-12 AB1157. Based on
improved measurements of DNA after treatment of exponential cultures with
rifampin, the cell mass per chromosomal replication origin (initiation
mass) and the time required to replicate the chromosome from origin to
terminus (C period) were determined. For these two strains, the initiation
mass approached values of 8 x 10(-10) and 10 x 10(-10) units of optical
density (at 460 nm) of culture mass per oriC, respectively, at growth rates
above 1 doubling/h (at 37 degrees C). The amount of protein per oriC
decreased with increasing growth rate for AB1157 and remained nearly
constant for the B/r strain. The C period decreased for both strains in an
essentially identical manner from about 70 min at 0.6 doublings/h to about
33 min at 3 doublings/h. From the initiation mass and C period, relative or
absolute copy numbers for genes with known map locations can be accurately
determined at different growth rates. At growth rates above 2 doublings/h,
when chromosomes are highly branched, genes near the origin are about
threefold more prevalent than genes near the terminus. At a growth rate of
0.6 doubling/h, this ratio is only about 1.7, which reflects the lower
degree of chromosome branching.
Copyright © 1998, American Society for Microbiology
Initiation and velocity of chromosome replication in Escherichia coli B/r and K-12 [In Process Citation]
Molecular and Cell Biology Programs, University of Texas at Dallas, Richardson 75083-0688, USA.
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