Showing papers by "Nancy Kleckner published in 1985"
TL;DR: It is suggested that IS10 transposition may preferentially occur immediately after passage of a chromosomal replication fork, and evidence is presented that the promoter and inner terminus of IS10 are coordinately activated in a dam-dependent fashion, presumably because they are hemimethylated at the same time.
324 citations
TL;DR: 40 mutants of E. coli K12, designated tex, are isolated, which increase the frequency of Tn10 precise excision and 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.
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.
81 citations
TL;DR: Tn10 is protected from fortuitous activation; high levels of transcription from an upstream promoter actually decrease its rate of transposition, providing additional evidence that Tn10 has evolved specific mechanisms for keeping its transposition activity low.
64 citations
TL;DR: Observations in complemented transposition of defective Tn10 elements off small multicopy plasmids find that length dependence in this situation is either reduced or absent, depending on the specific class of transposition events involved.
Abstract: The transposition frequencies of Tn10 elements from the bacterial chromosome to an F epitome decrease 40% for every kilobase increase in transposon length. The basis for this relationship is not known. We have now examined complemented transposition of defective Tn10 elements off small multicopy plasmids. We find that length dependence in this situation is either reduced or absent, depending on the specific class of transposition events involved. These observations can be interpreted as evidence against the model that chromosomal length dependence occurs because of decay of a transposition-associated replicative complex. This interpretation is consistent with unrelated experiments suggesting that Tn10 transposition is normally nonreplicative. Alternative explanations of length dependence phenomena are discussed.
28 citations