Involvement of multiple translocating DNA segments and recombinational hotspots in the structural evolution of bacterial plasmids

摘要: Previous studies from our laboratory (Kopecko & Cohen, 1975) have shown that two different antibiotic resistance-coding segments of the pSC50 plasmid are capable recA-independent translocation to small non-conjugative pSC101. Both transposable units structurally defined DNA containing 130 145-nucleotide long inverted repeat sequences at each end. The present electron microscope heteroduplex investigations indicate one genetic elements (TnA) is contained within length other (TnS) on both parental and recombinant plasmids. movement TnA TnS among plasmids as discrete structural implies specific sites their termini involved in process. Although multiple insertion for these exist pSC101 plasmid, non-random distribution recipient loci suggests site-specific it may involve recognition a frequently recurring nucleotide sequence. In addition role intergenomic transfer sequences, can serve hotspots types recombinational events: R1-19 Km-Nm resistance segment separates right terminus an IS1 (insertion sequence) element be deleted spontaneously, bringing juxtaposition. Recombination another repeats gene occurs left TnS. Our findings suggest evolutionary divergence several groups related cointegrated has occurred segmentally by series site events involving translocation, insertion, and/or deletion DNA.