Regulation and expression of the bacteriophage Mu mom gene: mapping of the transactivation (Dad) function to the C region

Abstract

Expression of the bacteriophage Mu mom gene is under tight regulatory control. One of the factors required for mom gene expression is the ( trans-acting function (designated Dad) provided by another Mu gene. To facilitate studies on the signals mediating mom regulation, we have constructed a mom-lacZ fusion plasmid which synthesizes β-galactosidase only when the Mu Dad transactivating function is provided. λpMu phages carrying different segments of the Mu genome have been assayed for their ability to transactivate β-galactosidase expression by the fusion plasmid. The results of these analyses indicated that the Dad transactivation function is encoded between the leftmost EcoRI site and the lys gene of Mu; this region includes the C gene, which is required for expression of all Mu late genes. Cloning of an approx. 800-bp fragment containing the C gene produced a plasmid which could complement Mu C − phages for growth and could transactivate the mom-lacZ fusion plasmid to produce β-galactosidase. These results suggest that the C gene product mediates the Dad transactivation function.