Location and analysis of nucleotide sequences at one end of a putative lac transposon in the Escherichia coli chromosome

Abstract

A segment of Escherichia coli DNA that contained a discontinuity of homology with Salmonella typhimurium DNA was isolated. The segment, 1,430 base pairs long, was derived from one end of the lac "loop," a region of about 12 kilobase pairs of E. coli DNA, including the lac operon which has no detectable homology with S. typhimurium DNA (K. Lampel and M. Riley, Mol. Gen. Genet. 186:82-86, 1982). The nucleotide sequence of the 1,430-base-pair segment of DNA was determined. The location of the junction of discontinuity of homology within the segment was established by hybridization experiments. Nucleotide sequences at or near the junction were determined to be similar to sequences that are involved in site-specific inversion in S. typhimurium, E. coli, phage P1, and phage Mu. Similar sequences are also present within the terminal inverted repeat sequences of transposon TnS and at the V-D-J joining sequences of eucaryotic immunoglobulin genes. Therefore, the lac operon, together with flanking DNA, may have been inserted into the E. coli chromosome at one time via a sitespecific recombination event. Rearrangement events of this kind undoubtedly have played a significant role in the evolutionary divergence of chromosomal DNAs.

Characterization of the Escherichia coli codBA operon encoding cytosine permease and cytosine deaminase

“…IC and the sequence of one strand is given in Fig, 2. A computer search revealed that the 1426 bp Pst\-Pvu\\ fragment present on pSD112 (open bar in Fig, 1C) had previously been sequenced by Buvinger et al (1984) in a study of the discontinuity of homology with S, typhimurium DNA.…”

The XbaI-BlnI-CeuI genomic cleavage map of Salmonella paratyphi B

“…In addition, small insertions or deletions distinguish the linkage maps of E. coli and S. typhimurium (15,33,34). For example, E. coli ferments lactose, while S. typhimurium is Lac-; loops of DNA which carry several genes, including lac, are present in E. coli but missing from S. typhimurium (7,16). More data are needed to clarify the relative roles of sequence divergence in homologous genes and chromosomal rearrangements in the evolution of different genera.…”

Insertion element IS121 is near proA in the chromosomes of Escherichia coli K-12 strains

“…These events are reasonably described by recA-dependent recombination between pairs of insertion elements.There are features of the proA-purE region of the chromosome that are not explained by the mechanisms associated with the mapped copies of IS], IS2, IS3, and IS5 in the region. These features include the discontinuities in homologies between the proA-proC regions of E. coli K-12 and Salmonella typhimurium (3,11,14) and some categories of chromosomal deletions.Recently, a new insertion sequence, IS121 (possibly identical to IS30 [9]), has been reported as a component of the Mu dIl(Ap lac) bacteriophage (12). At least three copies of this 1.2-kb element appear in the chromosomes of several E. coli K-12 strains.…”

“…There are features of the proA-purE region of the chromosome that are not explained by the mechanisms associated with the mapped copies of IS], IS2, IS3, and IS5 in the region. These features include the discontinuities in homologies between the proA-proC regions of E. coli K-12 and Salmonella typhimurium (3,11,14) and some categories of chromosomal deletions.…”

“…Such mechanisms would imply common types of insertion elements in E. coli and S. typhimurium; however, it is known that the S. typhimurium insertion element IS200 is absent from E. coli (10) and that the E. coli element IS5 is not present in S. typhimurium (17). It may be that insertion elements are unusually abundant near the proA-lac region of the E. coli K-12 chromosome because this region is an unusually receptive target and that the unusual receptivity is related to other recombination mechanisms that also have led to the observed sequence divergence between the two organisms in this region (e.g., the insertions in E. coli K-12 [3]).…”