Spontaneous and 9-aminoacridine-induced frameshift mutagenesis: second-site frameshift mutation within the N-terminal region of the lacI gene of Escherichia coli |
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Authors: | Alasdair J E Gordon Jennifer A Halliday Michael J Horsfall and Barry W Glickman |
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Institution: | (1) Department of Biology, York University, 700 Keele Street, M3J 1P3 Toronto, Ontario, Canada |
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Abstract: | Summary A novel forward mutational system, based on the acquisition of an Iq-d dominant phenotype from an initial Iq− recessive state, was used to identify second-site frameshift mutation ±1(±3
n
) events] within the N-terminal region of thelacI gene ofEscherichia coli. The DNA sequences are described of forty-six spontaneous and twenty 9-aminoacridine(9-AA)-induced second site mutations.
Although −1 frameshift events dominate both spectra, the nature and site specificity of these events clearly distinguish two
mutational distributions. The spontaneous distribution contains two −(A: T) frameshift hotspots; one within a monotonic A5 run (9 occurrences), the other at a 5′-CACAACAAC-3′ sequence (12 occurrences). In contrast 17 of the 20 mutations recovered after 9-AA treatment involve the loss of a
G: C pair, 14 of which occur at a single site (5′-CGGGC-3′). The striking specificity of the observed mutational hotspots is of interest since this open genetic target contains
similar sequences which were infrequently recovered. |
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Keywords: | Spontaneous frameshifts 9-Aminoacridine mutagenesis Translation reinitiation Negative complementation E coli lacI q-d mutants |
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