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In a particular genetic system, selection stimulates reversion of a lac mutation and causes genome-wide mutagenesis (adaptive mutation). Selection allows rare plated cells with a duplication of the leaky lac allele to initiate clones within which further lac amplification improves growth rate. Growth and amplification add mutational targets to each clone(More)
Prokaryotes are capable of sophisticated sensory behaviors. We have detected sequence motifs in bacterial signaling proteins that may act as transmitter or receiver modules in mediating protein-protein communication. These modules appear to retain their functional identities in many protein hosts, implying that they are structurally independent elements. We(More)
The eut operon of Salmonella typhimurium encodes proteins involved in the cobalamin-dependent degradation of ethanolamine. Previous genetic analysis revealed six eut genes that are needed for aerobic use of ethanolamine; one (eutR), encodes a positive regulator which mediates induction of the operon by vitamin B12 plus ethanolamine. The DNA sequence of the(More)
During growth under selection, mutant types appear that are rare in unselected populations. Stress-induced mechanisms may cause these structures or selection may favor a series of standard events that modify common preexisting structures. One such mutation is the short junction (SJ) duplication with long repeats separated by short sequence elements:(More)
In the lac adaptive mutation system of Cairns, selected mutant colonies but not unselected mutant types appear to arise from a nongrowing population of Escherichia coli. The general mutagenesis suffered by the selected mutants has been interpreted as support for the idea that E. coli possesses an evolved (and therefore beneficial) mechanism that increases(More)
The cheA locus of Escherichia coli encodes two similar proteins, CheAL (654 amino acids) and CheAS (557 amino acids), which are made by initiating translation from different in-frame start sites [start(L) and start(S)]. CheAL plays an essential role in chemotactic signaling. It autophosphorylates at a histidine residue (His-48) and then donates this(More)
Adenosylcobalamin (Ado-B12) is both the cofactor and inducer of ethanolamine ammonia lyase (EA-lyase), a catabolic enzyme for ethanolamine. De novo synthesis of Ado-B12 by Salmonella enterica occurs only under anaerobic conditions. Therefore, aerobic growth on ethanolamine requires import of Ado-B12 or a precursor (CN-B12 or OH-B12) that can be adenosylated(More)
The cheA locus of Escherichia coli encodes two protein products, CheAL and CheAS. The nucleotide sequences of the wild-type cheA locus and of two nonsense alleles confirmed that both proteins are translated in the same reading frame from different start points. These start sites were located on the coding sequence by direct determination of the(More)
Duplications are often attributed to "unequal recombination" between separated, directly repeated sequence elements (>100 bp), events that leave a recombinant element at the duplication junction. However, in the bacterial chromosome, duplications form at high rates (10(-3)-10(-5)/cell/division) even without recombination (RecA). Here we describe 1800(More)