Mutations in the dnaA gene of E. coli are lethal and canonly be studied following the isolation of conditional,temperature-sensitive mutations. Such mutant strains grownicely and replicate their DNA at the permissive temperatureof 18°C, but they do not grow or replicate their DNA at therestrictive temperature of 37°C. Two observations were usefulin determiningthe function of the DnaA protein product.First, in vitro studies using DNA templates that haveunwound do not require the DnaA protein. Second, if intactcells are grown at 18°C and are then shifted to 37°C, DNAsynthesis continues at this temperature until one roundof replication is completed and then stops. What do theseobservationssuggest about the role of the dnaA gene product?
Mutations in the dnaA gene of E. coli are lethal and can
only be studied following the isolation of conditional,
temperature-
sensitive mutations. Such mutant strains grow
nicely and replicate their DNA at the permissive temperature
of 18°C, but they do not grow or replicate their DNA at the
restrictive temperature of 37°C. Two observations were useful
in determining
the function of the DnaA protein product.
First, in vitro studies using DNA templates that have
unwound do not require the DnaA protein. Second, if intact
cells are grown at 18°C and are then shifted to 37°C, DNA
synthesis continues at this temperature until one round
of replication is completed and then stops. What do these
observations
suggest about the role of the dnaA gene product?
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