Deletions, rearrangements and tandem duplications of recombinant plasmids containing yeast ribosomal DNA.

Recombinant DNA plasmids, formed by the insertion of yeast ribosomal DNA into Escherichia coli plasmids pSC101 or pMB9, underwent deletions, rearrangements and tandem duplications. Independently derived deletion products of plasmids, constructed using pMB9 as a vector, are indistinguishable from each other. These deletion products from multimers composed of tandem repeats. In at least one case a plasmid, constructed by inserting an SmaI fragment of yeast ribosomal DNA into pSC101, underwent deletion and rearrangement to form a product in which a segment, consisting of part of the pSC101 sequence and part of the yeast ribosomal DNA sequence, was duplicated to form a tandem repeat. Deletion and rearrangement take place in Rec+, recA- and recB- recC- cells. The rate of deletion in Rec+ cells is higher than in recA- cells. The rate of deletion in minicell-producing, X-ray resistant strains is much higher than in other Rec+ strains.