Fig. 1. Replacement of the vatM promoter with the act6 promoter. Panel A shows the plasmid pVATM-act6, which contains segments of the vatM promoter and coding region separated by the selectable marker pyr5-6 and the act6 promoter. Panel B illustrates the predicted outcome of homologous recombination between the chromosomal vatM gene and a linearized segment of pVATM-act6, following its transformation into DH1 cells. Panel C shows a Southern blot of genomic DNA from DH1 (D) and one of the transformants (V). The genomic DNA was digested with BclI and probed to detect vatM. This transformant, which was given the name VatMpr, displayed an increased restriction fragment size consistent with the double crossover event illustrated in B.