Mismatch Repair Mutations of ESCHERICHIA COLI K12 Enhance Transposon Excision (original) (raw)

Abstract

Excision of the prokaryotic transposon Tn_10_ is a host-mediated process that occurs in the absence of recA function or any transposon-encoded functions. To determine which host functions might play a role in transposon excision, we have isolated 40 mutants of E. coli K12, designated tex, which increase the frequency of Tn_10_ precise excision. Three of these mutations (tex_A) have been shown to qualitatively alter RecBC function. We show that 21 additional tex mutations with a mutator phenotype map to five genes previously identified as components of a methylation-directed pathway for repair of base pair mismatches: uvrD, mutH, mutL, mutS and dam. Previously identified alleles of these genes also have a Tex phenotype.—Several other E. coli mutations affecting related functions have been analyzed for their effects on Tn_10 excision. Other mutations affecting the frequency of spontaneous mutations (mutT, polA, ung), different excision repair pathways ( uvrA, uvrB) or the state of DNA methylation (dcm) have no effect on Tn_10_ excision. Mutations ssb-113 and mutD_5, however, do increase Tn_10 excision.—The products of the mismatch correction genes probably function in a coordinated way during DNA repair in vivo. Thus, mutations in these genes might also enhance transposon excision by a single general mechanism. Alternatively, since mutations in each gene have qualitatively and quantitatively different effects on transposon excision, defects in different mismatch repair genes may enhance excision by different mechanisms.

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Selected References

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