Recombination in the lambda repressor gene: evidence that very short patch (VSP) mismatch correction restores a specific sequence |
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Authors: | M Lieh |
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Institution: | (1) Department of Microbiology, University of Southern California, School of Medicine, 90033 Los Angeles, CA, USA |
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Abstract: | Summary The mutation am6 in the cI gene of bacteriophage is identified as a C T transition in a 5 CC
T
A
GG sequence. In four-factor crosses of am6 with nearby mutations in cI, the frequencies of cI+ recombinants are much higher than expected from the physical distances. A very short patch (VSP) mismatch repair system is presumed to recognize am6/am
+ mispairs in the heteroduplexes that accompany recombination between the outside markers. Mutation am6 is corrected to am
+; correction of am
+ to am6 was not detected. Clear-plaque mutation 1-1 in cI is a T C transition in a 5 CTTGG sequence, resulting in the sequence 5 CC
T
A
GG. When 1-1 was crossed with nearby mutations in gene cI, there were no excess cI+ recombinants, which would result from repair of CCTGG (1-1) to CTTGG (cI+). However, in crosses of cI+ phages with mutation 1-1, there was an excess of cI- recombinants, indicating that cI+ was repaired to 1-1. Preferential repair does not require adenine or cytosine methylation: when repairing a mismatch, the VSP repair system apparently identifies specific mispaired bases by sequence alone. |
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Keywords: | |
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