Figure 4.

Complementation of HU-Lacking E. coli Mutants by HC.

(A) Effect of HC on the cell morphology of HU-lacking E. coli mutants. HU+, wild-type strain (JR1669); HU−, mutants lacking HU (JR1672); HU−/HC-expressing vector, pQE50-CmhupA mutants lacking HU carrying HC-expressing vector; HU−/parent vector, pQE50 mutants lacking HU carrying parent vector. Strains were grown in Luria-Bertani (LB) medium containing an appropriate antibiotic at 37°C. HU−/pQE50-CmhupA and HU−/pQE50 were grown in the presence of the inducer isopropylthio-β-galactoside (IPTG). Cells were fixed in 0.5% glutaraldehyde, stained with 1.0 μg/mL DAPI, and visualized by phase-contrast and fluorescence microscopy. Bar = 3 μm for all panels.

(B) Effect of HC on the cold-sensitive growth phenotype of HU-lacking E. coli mutants. Strains were grown to log phase in LB medium containing appropriate antibiotic and IPTG. They were transferred to 0°C for various periods and plated on LB agar containing appropriate antibiotic and IPTG. The plates were incubated at 37°C overnight, and the number of colonies was scored. The colony number was set at 1.0 immediately before transfer.