FIG. 3.

Comparative Southern analysis of the wild-type and mutant lacS loci. Chromosomal DNAs digested with EcoRI (two left lanes of each gel) and XbaI (two right lanes of each gel), identifying the lacS locus in S. solfataricus Gθ (P) and in the LacS⁻ mutant GθW (M), were hybridized with DNA fragments progressively covering the upstream and downstream regions of the lacS coding sequence in independent experiments. The extended 15-kbp region used as a source of these probes is represented in the middle as a solid bar containing already-identified ORFs (xylS, lacS, and lacTr) or putative protein-encoding sequences (ABC, ABC transporter) in their relative orientations. On the left, two arrows indicate the sizes corresponding to the differential cross-hybridization signals on the EcoRI digests hybridized with the extreme 5′ DNA fragment used in the analysis.