FIG. 1.

Deletions from the croRS locus. (A) Map of the wild-type locus of E. faecalis JH2-2 and location of the DNA fragments (H1A, H1B, and H2) used for allele exchange by homologous recombination. Numbers in parentheses indicate the coordinates of the extremities of the croR, croS, and serS open reading frames (open arrows), of the H1A, H1B, and H2 DNA fragments (hatched), and of a portion of the rrnC rRNA gene cluster (open box). BglII restriction sites were introduced at one extremity of H1A, H1B, and H2. (B) Replacement of croRS by an erythromycin resistance gene cassette (erm). JH2-2ΔcroRS/erm was obtained by homologous recombination between the wild-type croRS locus of JH2-2 and a derivative of the thermosensitive plasmid pHS1 carrying the H1A-erm-H2 DNA insert depicted in the inset. (C) To construct JH2-2ΔcroRS, the erm cassette was deleted from the chromosome of JH2-2ΔcroRS/erm by allele exchange with H1A directly linked to H2. (D) To construct JH2-2ΔcroS, the erm cassette of JH2-2ΔcroRS/erm was replaced (using H1B linked to H2) by the croR open reading frame. Numbers in parentheses indicate the extremities of the deletions from JH2-2ΔcroRS and from JH2-2ΔcroS. Coordinate 1 corresponds to position 3,169,253 of the assembled E. faecalis genome at www.tigr.org.