FIG. 2.

Cell morphology following loss of the EcoRI RM gene complex. E. coli strains AB1157 (rec⁺) and JC5519 (recB21 recC22) carrying pIK172 (pSC101Ts, EcoRI r⁺ m⁺, Ap^r) or pIK173 (its r⁻ version) were aerated at 30°C in L broth with selective antibiotics to an optical density of 0.3 at 660 nm. Then the antibiotics were removed, and the culture was transferred to 42°C with aeration as described for Fig. 1. Cells were harvested at the indicated time intervals after the temperature shift and mixed with the same volume of methanol-HCO₂H (2:1). After incubation on ice for 10 min, cells were collected by centrifugation, resuspended in 10 mM Tris-HCl (pH 7.5)–10 mM MgSO₄, stained with DAPI, and observed under a microscope.