FIG. 2.

Promoter strengths and interactions. The SalI-SnaBI restriction fragment, with the mutations and in the orientations indicated, was cloned in front of the promoterless lacZ gene of pMRR9 (13) and transferred as a single copy to the chromosome of MC1061.5 (13) using the reporter system of Simons et al. (25) as previously described (13). The β-galactosidase activity (Miller units) was determined (13) for each of these strains, transformed with either the CII expression plasmid (pPN72)(13) or its cII⁻ derivative (pPN178 13). Values shown are the means for six individual cultures of each strain on the same day. Errors are 90% confidence limits determined by the Student t test (27). The values determined for four independent single lysogens of the same clone varied by less than 10%. Background activity (1 U) was subtracted from the activities shown and was determined by measuring the β-galactosidase activity of MC1061.5 lysogenized with λpMRR9 and transformed with either pPN72 or pPN178. Coordinates of the restriction sites refer to the numbers of base pairs from the left end of the chromosome of 186 (GenBank accession number U32222). n.d., not determined.