Similarity of vegetative map and prophage map of bacteriophage Mu-1

Abstract

The vegetative map of bacteriophage Mu was extended by the localization of three more amber mutations belonging to different complementation groups, and the position of the c gene on the vegetative map was approximately determined. The data confirm the previous finding that the vegetative map is linear (Wijffelman et al., 1972). Defective Mu lysogens were isolated from an Escherichia coli K12 strain, which has an insertion of Mu in the trp operon, by selecting for TonB colonies. All these defective lysogens were no longer immune to Mu infection, suggesting that the gene controlling immunity is located near to the end of the prophage proximal to tonB. By analyzing the remaining prophage genes in the defective lysogens, it was possible to determine the order of 16 amber mutations belonging to different complementation groups. The results show that the position of the genes on both the vegetative map and the prophage map is the same. The prophage map of Mu was determined by using the same method in another 9 independently isolated insertion mutants. In 7 of these mutants the gene order in the prophage is the same as found for the above-mentioned strain. The other two contain the prophage genes in the reversed order. All defective lysogens derived from these two insertion mutants by selection for TonB colonies were immune. The results show that Mu is integrated in a unique way and that both orientations may occur. The similarity between prophage map and vegetative map and the consequence for the mechanism of the integration process are discussed.