FIG. 4.

Chromosome replication and dnaA gene expression following a temperature downshift. Strain BBC119 was grown under conditions of balanced growth in AB-glucose-Casamino Acids medium at 37°C, and part of the culture was shifted to 14°C at the time indicated by the arrow. (A) Growth was followed by measurement of OD₄₅₀, and the culture was diluted when the OD₄₅₀ reached 0.5. (B) Samples were taken for measurement of origins per light scatter (LS), DNA per light scatter, and DnaA–β-galactosidase specific activity. Origins per light scatter was determined in samples incubated with rifampin and cephalexin at 37°C. Open symbols, 37°C; black symbols, 14°C; gray symbols, steady-state 14°C values.