THE PROXIMITY OF MINI-MU-TERMINI CAN AFFECT THE PRODUCTS OF DNA TRANSPOSITION

Temperate bacteriophage Mu's 37 kilobase pair (kb) linear, double-stranded DNA requires DNA sequences at both termini in cis to transpose in a duplicative manner and thus propagate its genome during the lyric cycle. To define any spatial or orientation parameters between these sequences, we constructed ''isomer'' plasmids pMD186 and pMD861 containing identical Mu termini in close (or inverse) orientation 407 base pairs apart, or separated by 9.3 kb of plasmid pSC101 DNA, respectively. Both mini-Mu plasmids transposed at equal frequencies onto an F' episome in vivo, in the presence of an induced helper Mu prophage. However, while the ast majority of pMD861 mini-Mu transposition and maturation events were found to be the result of duplicative transposition (cointegrates), virtually all pMD186 transpositions yielded simple Linear insertions of the mini-Mu plasmid without concomitant duplication of the mini-Mu. However, the construction of pMD186 mini-Mu plasmid derivatives, containing increased lengths of DNA sequences cloned between the ends of the Mu genome, yielded increasing frequencies of duplicative transposition products. These results suggest that the distance between the Mu termini can affect the final outcome of the transposition reaction.