Specific stimulation of recA-independent plasmid recombination by a DNA sequence at a distance.

Recombination between directly repeated DNA sequences can occur via both recA-dependent and recA-independent mechanisms. They are differentially affected by the length of the repeat and the distance separating the repeats, respectively. Interestingly, a 623 base-pairs long DNA sequence of the plasmid pBR322 was found to stimulate specifically recA-independent recombination between tandem repeats. Analysis of this stimulating sequence has revealed the following features. (1). It is cis-acting. (2). No specific region of it appears to be essential for the effect. Moreover, a neutral sequence of comparable size was able to substitute for the sequence in influencing recombination. (3). The sequence affects recombination between tandem repeats within the tetA but not the bla gene of pBR322. (4). The sequence exerts its effect in a position-dependent manner. (5). It changes not only the frequency but also the products of recombination. Our results provide an example that recA-independent recombination can be influenced by DNA sequences at a distance.