Regulation of bacteriophage mu and mini-mu DNA replication in vivo.

To study the regulation of bacteriophage Mu DNA's integrative-replication (transposition) during lytic growth in a cell containing both a Mu and a helper-dependent Mini-Mu (short, internally-deleted Mu genome), we placed "marker" genes (bla, lacZ) within either genome and then measured their encoded enzymes as indicators of the gene dosage. These results, corroborated using DNA-DNA hybridization, show that Mu and Mini-Mu DNA transposition is well regulated, requires both the Mu A and B gene products, and can be readily monitored by measuring beta-galactosidase and beta-lactamase expressed from the lacZ and bla genes, respectively.