Table 1.

Effect of denB expression on E.coli growth

Plasmid	No. of colonies formed at 30°C	No. of colonies formed at 42°C	30°/42°C ratio
pBRdenBam	795a	281 × 104	2.8 × 10−4
pBR322	309 × 104	445 × 104	0.69

The effect of denB expression on E.coli cell growth was examined as described in Materials and Methods. Data are means from three independent experiments.

^aA total of 156 colonies formed at 30°C by cells transformed with pBRdenB^am was tested for colony-forming ability on LB-Thy or LB-Thy-Amp agar plates at 42°C. Cells of all the original 156 colonies formed colonies on the LB-Thy agar plate at 42°C, but cells of 154 of these 156 original colonies (∼99%) did not form colonies on the LB-Thy-Amp agar plate at 42°C, indicating that most of the original colonies formed at 30°C consisted of cells lacking pBRdenB^am.