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Generation of Single Base-Pair Deletions, Insertions, and Substitutions by a Site-Specific Recombination System
John M. Leong, Simone E. Nunes-Duby and Arthur Landy
Proceedings of the National Academy of Sciences of the United States of America
Vol. 82, No. 20 (Oct. 15, 1985), pp. 6990-6994
Published by: National Academy of Sciences
Stable URL: http://www.jstor.org/stable/26747
Page Count: 5
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The sequence analysis of both products of individual φ 80 site-specific recombination events in vivo shows that recombination with a secondary attachment (att) site generates several different novel joints at the mismatched position: one recombination event resulted in a single base-pair deletion and two other recombination events resulted in two different single base-pair substitutions. The characterized products of recombination can be straightforwardly interpreted as the outcome of strand exchange involving staggered nicks bracketing the heterology within an overlap region of five to nine base pairs. In comparison, more complex segregation patterns have been observed in previous studies of λ recombination between nonidentical att sites; the nature of the overlap region heterology may have a significant effect on the segregation patterns. To recover both products of a single recombination event, we used a plasmid that carries the φ 80 int and xis genes and both att sites. Because the two att sites are situated in opposite orientation, intramolecular recombination between them inverts rather than deletes the intervening segment of DNA. Although subsequent reinversion restores the original gross genetic arrangement, single base-pair insertions, deletions, and substitutions are introduced at the sites of recombination. One of the mutations improves the recombination efficiency of the secondary att site and thereby converts a formerly ``stable'' sequence to an efficient target for rearrangement, and other mutations are predicted to alter the specificity of recombination. These pathways may also provide useful models for the efficient generation of localized sequence diversity on a developmental (as well as evolutionary) time scale.
Proceedings of the National Academy of Sciences of the United States of America © 1985 National Academy of Sciences