Transposition and replication of maxi-Mu derivatives of bacteriophage Mu.

The insertion of DNA fragments within the lac sequence of a MudI(Ap,lac) prophage resulted in the formation of a set of maxi-Mu genomes which were 39.8, 59, 85.6, and 88.2 kb long, respectively. The comparison of these maxi-Mu's with the 37.2-kb-long parental MudI(Ap,lac) indicated that the transposition frequency decreased as the length of the prophage increased. No replication of the two longest maxi-Mu's could be detected. The 59- and the 39.8-kb-long chimeric genomes were noted to replicate at approximately 1-2 and 30%, respectively, of the rate found with the MudI(Ap,lac) prophage. The length dependence of the transposition and replication could be explained by the impairment of an early step of the transposition/replication mechanism.