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A fine structure map of spontaneous and induced mutations in the lambda repressor gene, including insertions of IS elements
Authors:M. Lieb
Affiliation:(1) Department of Microbiology, University of Southern California, School of Medicine, 90033 Los Angeles, California, USA
Abstract:Summary Mutations at over 70 sites in the cI gene have been mapped by 4-factor crosses and assigned precise or approximate positions in the DNA sequence. 16 of 25 spontaneous mutations were insertions of IS1, IS3 or IS5 into AT-rich regions of cI. The 5-methylcytosine in the sequence Cm5CAGG is a hot spot for spontaneous cI amber mutations. Recombination frequencies between mutations were proportional to distance with the exception of amber mutations at 4 sites, including the host spot for spontaneous mutations. Mutations with a given phenotype are clustered on the genetic map. No missense mutations affecting repressor activity were found in the central one-third of cI, but 5 of 6 ind- mutations were located in this region. The aminoterminal third of the gene contains the sites of most trans-dominant cI- mutations, and of all ts mutations that result in repressors that are reversibly inactivated at high temperatures.
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