Transduction of Merodiploidy: Induced Duplication of Recipient Genes

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Abstract
Escherichia coli PB160, which carries a tandem duplication with the gene order metB + argH − su 159 + thi + : metB + argH + su 159 − thi + , was used to study the mechanism of P1 transduction of genes in the duplicated region. Transduction of the su 159 + allele contained within the duplicated segment yields two kinds of su 159 + recombinants: 91% are haploid su 159 + and 9% are su 159 + / su 159 − merodiploids. The duplication in these merodiploid transductants includes the metB locus; however, both copies of the metB locus usually are derived from the recipient. Thus, the requirements for transduction of the “condition of merodiploidy” appear to be the cotransduction of the repeat point (the region where the duplication begins to repeat itself) and, of course, the selected marker (in this case su 159 + ). A mechanism whereby two recipient chromosomes interact with the transduced “repeat point” region to regenerate the tandem duplication is implicated. It appears that a duplication much larger than the quantity of genetic material carried by a P1 phage can be produced in a transductant.