FIG. 2.

Construction of insertion and deletion alleles by assembly of three fragments with overlapping ends. Half arrows indicate the positions of the primers, whose sequences are given in Table 1. Segments A and C represent DNA segments flanking the locus to be deleted or the site of insertion (depending on needs of experiment). Segment B represents (i) the erm (resistance) gene used initially to replace the mdaB locus; (ii) the rpsL streptomycin susceptibility gene from C. jejuni that was inserted just upstream of erm in a strain carrying erm in place of mdaB; or (iii) the rpsL,erm cassette, which can be moved to many loci.