Figure 1.

Detection of mutants that did not exhibit rapid decrease of colony forming ability in the stationary phase. (A) E. coli strain BL21 was transformed with pGEX-SUP35NM, and colony forming ability was examined as described in Materials and Methods. In a majority of cases colony forming ability decreased quickly (solid line), but there were cases (at a frequency of about a 5% of the trials) in which the colony forming ability temporarily increased; of a total of eight such cases, three are shown in this figure (dotted lines). (B) From each of the eight exceptional cases, a representative clone was picked, inoculated in fresh growth medium, and examined for colony forming ability as before; only the three clones corresponding to the exceptional cases shown in Figure 1A are shown.