The control of expression of the Bacillus subtilis spoIIA locus was analyzed by titrating gene expression against gene copy number. A plasmid integrated into the B. subtilis chromosome and carrying the spoIIA control region fused to Escherichia coli lacZ was forced to form tandem repeats by the selection of clones that grow on high levels of chloramphenicol, the antibiotic against which the plasmid determines resistance. DNA from the clones was digested with BglII, which did not cut in the reiterated region, and the size of the fragment was determined by orthogonal-field-alternation gel electrophoresis to determine the copy number. Most clones had fairly homogeneous copy numbers. Gene expression was monitored by beta-galactosidase activity. The results indicate that spoIIA was under positive control by a moiety present at about five copies per chromosome. Spore formation was not affected by amplification, so spoIIA-lacZ reiteration did not sequester a molecule required elsewhere for sporulation
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