Figure 2.

(a) Effect of addition of chloramphenicol (Left) or kasugamycin (Right) upon accumulation of the lacZΔ mRNA (see Materials and Methods for details). At the indicated time after drug addition, the lacZΔ mRNA was visualized in total RNA from ENS32 cells by using Northern blots. The position of the full-length operon transcript (4.2 kb) and of a processed species corresponding to the lacZ mRNA proper (3.2 kb), as well as that of the 23S and 16S rRNAs, are indicated. Controls showed that MO00, the parent strain lacking the P_T7–lacZΔ construct, produced no lac-hybridizing signal under these conditions (cf. 21). (b) Northern blot showing the decay of the lacZΔ mRNA in control cells (Left) or in cells that have been treated with kasugamycin for 20 min (Right). At zero time, transcription has been switched off by transferring the cells to an identical medium lacking IPTG. All symbols are as in a.