Disease relevance of lexA

• DNA polymerase I* is a form of the DNA polymerase I isolated from Escherichia coli which are expressing recA/lexA (SOS) functions [1].
• This sequence is also present upstream of the Geobacter metallireducens lexA gene, indicating that it is the LexA box of this bacterial genus [2].
• 2AP-reactivation can be distinguished from Weigle-reactivation in that it is not accompanied by an increase in mutagenesis, does not act on the single-stranded DNA bacteriophage phi X174, and occurs in recA and lexA bacteria [3].
• The plating efficiency of UV-irradiated lambda-phage was drastically reduced in the lexA and recA strains treated with Blm [4].
• By using this method, the lexA-like genes of Salmonella typhimurium, Erwinia carotovora, Pseudomonas aeruginosa, and P. putida were cloned [5].

High impact information on lexA

• Similar observations were made in studies of the E. coli LexA repressor and phage P22 C1 transcription activator proteins [6].
• During the SOS response, LexA repressor is inactivated by specific cleavage [7].
• The M. tuberculosis recA locus comprises an 85 kd open reading frame but produced 38 kd RecA and 47 kd products in E. coli [8].
• Molecular biology. recA: from locus to lattice [9].
• A human gene that shares homology with Escherichia coli recA (and its yeast homologue RAD51) has been cloned from a testis cDNA library, and its 37 kDa product (hRad51) purified to homogeneity [10].

Chemical compound and disease context of lexA

• Transient exposure of E. coli to 5-azacytidine for 60 min induced both recA-dependent inhibition of cell division and induction of lambda prophage in Dcm+ strains but not in Dcm- mutants [11].
• The dimerization domain of the LexA repressor has been replaced by two heterologous dimerization motifs: the "leucine zipper" from the jun oncogene product and the carboxy-terminal oligomerization domain of Escherichia coli lac repressor [12].
• The binding of Escherichia coli LexA repressor to the recA operator was examined as a function of the concentration of NaCl, KCl, NaF, and MgCl2 at pH 7.5, 21 degrees C. The effects of pH at 100 mM NaCl were also examined [13].
• The recA gene from Clostridium perfringens is induced by methyl methanesulphonate and contains an upstream Cheo box [14].
• beta-Galactosidase activities (beta-GA) of E. coli strains carrying the fusion gene of recA and lacZ, GE94 and its DNA repair-deficient derivatives such as KY946[uvrA], KY945[recA] and KY943[lexA] treated with UV, 4NQO, MNNG and MMC were examined [15].

Biological context of lexA

• Nucleotide sequence of the lexA gene of Escherichia coli K-12 [16].
• We have sequenced 943 base pairs of cloned E. coli DNA containing the lexA gene [16].
• AZT and ddA showed marginal effects in a DNA repair (preferential toxicity) assay in which E. coli WP2 and CM871 uvrA recA lexA were used [17].
• Tn5 insertion mutations in the lexA gene increased the frequency of plasmid recombination [18].
• Furthermore, DNA damage induces expression of the lexA-dinB transcriptional unit but not that of the recA gene [2].

Anatomical context of lexA

• A broad host-range expression plasmid was constructed comprising the incQ replicon, the recA promoter from Escherichia coli and the g10-L ribosome binding site (RBS) derived from bacteriophage T7 [19].

Associations of lexA with chemical compounds

• These include three branches that are blocked by the exrA, recB, or uvrD mutation, a fourth branch that is blocked by any of these mutations and is also sensitive to chloramphenicol treatment, and at least one additional branch that is not sensitive to either of these mutations or to chloramphenicol treatment [20].
• Therefore, we assume that cinnamaldehyde may enhance an error-free recombinational repair system by acting on recA-enzyme activity [21].
• Coumermycin A1, however, produced a more gradual decline in synthesis rate which is unaffected by defects in the recA or lexA genes [22].
• Furthermore, this mechanism might be indirectly related to the SOS regulon, because lexA and recA mutants, which block the induction of the SOS response, prevent dnaA induction by MMS and MC [23].
• Using two independent methods to detect pyrimidine dimers we found that UV irradiated RecA deficient cells removed dimers from their DNA more rapidly if they contained the lexA41 mutation than if they contained the wild-type lexA gene [24].

Enzymatic interactions of lexA

• RecF, RecO and RecR, three of the important proteins of the RecF pathway of recombination, are also needed for repair of DNA damage due to UV irradiation. recF mutants are not proficient in cleaving LexA repressor in vivo following DNA damage: therefore they show a delay of induction of the SOS response [25].

Regulatory relationships of lexA

• (1) The umuC gene is inducible by Blm and the induction is regulated by the lexA and recA genes [4].
• These results establish that uvrA is repressed by lexA in vivo whereas ssbA is not [26].
• The recA and sfiA genes of Escherichia coli are SOS operons regulated negatively by the LexA repressor [27].
• In vivo, we showed that recX is under control of the LexA repressor and is up-regulated in response to DNA damage [28].

Other interactions of lexA

• Furthermore, strains deficient in excision repair subsequent to the incision step (i.e., polA, rec, exrA) showed more double-strand breaks than the wild type strain [29].
• Reverse transcription-PCR analyses demonstrated that, in both cases, lexA and dinB constitute a single transcriptional unit [2].
• The mutants can be classified into three groups by the location of the mutations, umuA, umuB and umuC [30].
• In Escherichia coli, the cell division block observed during the SOS response requires the product of the sfiA gene, whose expression is regulated negatively by the LexA repressor and positively by the RecA protease [31].
• Clarification of the Escherichia coli genetic map in the 92-minute region containing the ubiCA operon and the plsB, dgk, lexA, and dinF genes [32].

Analytical, diagnostic and therapeutic context of lexA

• The interaction of the lexA repressor of E. coli with poly[d(A-T)] has been studied by circular dichroism [33].
• By means of genetic complementation tests it was demonstrated that the low levels of UV mutagenesis in lexA- strains and their thermosensitive derivatives result from the synthesis of a diffusible product [34].
• Electrophoretic mobility-shift assays demonstrated that X.c. pv. citri LexA interacts with the promoter region of X.c. pv. citri lexA, as well as with those of the recA genes of X.c. pv. citri and E. coli [35].
• The methyltransferases form tight binding complexes with azacytosine in DNA which could interfere with the recA recBCD repair pathway which is largely responsible for cell survival after treatment with the drug [36].
• Mass analysis using scanning transmission electron microscopy suggests that the site size of the LexA repressor on RecA is two, which would be consistent with a nearest-neighbor exclusion model for binding [37].

References