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. 1990 Jun;125(2):275–280. doi: 10.1093/genetics/125.2.275

A Set of Lacz Mutations in Escherichia Coli That Allow Rapid Detection of Specific Frameshift Mutations

C G Cupples 1, M Cabrera 1, C Cruz 1, J H Miller 1
PMCID: PMC1204017  PMID: 2199309

Abstract

We have used site-directed mutagenesis to alter bases in lacZ near the region encoding essential residues in the active site of β-galactosidase. The altered sequences generate runs of six or seven identical base pairs which create a frameshift, resulting in a Lac(-) phenotype. Reversion to Lac(+) in each strain can occur only by a specific frameshift at these sequences. Monotonous runs of A's (or of T's on the opposite strand) and G's (or C's) have been constructed, as has an alternating -C-G-sequence. These specific frameshift indicator strains complement a set of six previously described strains which detect each of the base substitutions. We have examined a variety of mutagens and mutators for their ability to cause reversion to Lac(+). Surprisingly, frameshifts are well stimulated at many of these runs by ethyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine and 2-aminopurine, mutagens not widely known to induce frameshifts. A comparison of ethyl methanesulfonate, N-methyl-N'-nitro-N-nitrosoguanidine and 2-aminopurine frameshift specificity with that found with a mutH strain suggests that these mutagens partially or fully saturate or inactivate the methylation-directed mismatch repair system and allow replication errors leading to frameshifts to escape repair. This results in a form of indirect mutagenesis, which can be detected at certain sites.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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