Effects of deletions on cotransduction linkage in Salmonella typhimurium: evidence that bacterial chromosome deletions affect the formation of transducing DNA fragments.

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The effect of nearby deletions on linkage between markers (all located on the same side of the deletion) was studied in two regions of the Salmonella typhimurium chromosome by bacteriophage P22-mediated transductions. A number of deletions significantly altered the frequency with which pairs of markers were jointly transduced. Since, in some cases, significant alterations in cotransduction linkage were observed when the same deletion was present in both donor and recipient, all such effects could not be ascribed to lack of homology caused by the deletion. In one case a significantly altered cotransduction frequency was noted when a deletion was located beyond the chromosomal region included on the selected transducing DNA fragments. This was observed when the deletion was present in both donor and recipient or in the donor alone but not when the deletion was present only in the recipient. These experiments indicate that some deletions alter cotransduction linkages because they affect the formation of the transducing particles, presumably by altering the proportion of transducing particles which carry both markers or by altering the position of the markers with respect to the ends of the transducing DNA fragments.