Specific mismatch correction in bacteriophage lambda crosses by very short patch repair (original) (raw)

Summary

In crosses under rec +, red +, gam + conditions, mutation _am_6 in the _c_I (repressor) gene of bacteriophage λ recombines with other _c_I mutations much more frequently than predicted by the physical distances involved. In four-factor crosses of _am_6 with mutations located 22–60 base pairs to the left, _c_I+ recombinants that are expected to require three crossovers (triple recombinants) are more frequent than recombinants that require only one crossover. However, when _am_6 is crossed with large insertions in _c_I, which may be expected to interfere with the formation of heteroduplexes by branch migration, the frequency of _c_I+ triple recombinants is very low. In addition, _c_I+ recombinants in crosses between _am_6 and adjacent mutations have a high probability of retaining the flanking markers of the _am_6 parent. These findings suggest that _am_6 is particularly susceptible to mismatch repair in heteroduplexes are presumed to be the result of branch migration from crossovers occurring at some distance from _am_6. The absence of co-repair when _am_6 is crossed with adjacent _c_I mutations indicates that most repair tracts extend no farther than about 20 bp to either side of the mismatch.

The _am_6 mutation arose in the glutamine codon in a CCAGG sequence, in which the central cytosines are methylated in K12 strains. Their location in methylated sequences may make certain amber mutations susceptible to a specific very short patch (VSP) repair.

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  1. Department of Microbiology, University of Southern California, School of Medicine, 90033, Los Angeles, CA, USA
    M. Lieb

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  1. M. Lieb
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Communicated by W. Arber

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Lieb, M. Specific mismatch correction in bacteriophage lambda crosses by very short patch repair.Molec Gen Genet 191, 118–125 (1983). https://doi.org/10.1007/BF00330898

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