title: Lethality of visible light for Escherichia coli hemH1 mutants influence of defects in DNA repair.
abstract: The hemH gene encodes ferrochelatase, the final enzyme of the heme biosynthetic pathway. Defects of this enzyme lead to accumulation of protoporphyrin IX and an increase in reactive oxygen species, causing susceptibility to blue and white light in bacteria and protoporphyria in humans. Here we show that the photosensitivity of hemH1 strains is much increased when the bacteria are devoid of ability to repair abasic sites. The sensitivity is increased 10- or 50-fold, in mutants bearing single xth or triple xth-nth-nfo mutations, respectively, but is not changed in mutants bearing nth, fpg, mutY, and mutT that are positive or negative for uvrA. This may indicate that in hemH1 mutants abasic sites are accumulated to a greater degree than oxidised bases, and/or that protoporphyrin, in the presence of abasic sites, increases the photosensitivity of hemH1 cells. It was shown in this work that the level of abasic sites (and/or strand breaks) in DNA of hemH1 strains increases greatly. Abasic sites and oxidative bases are potential mutagenic lesions. Nevertheless, the sensitivity of hemH1 bacteria to the lethal effect of visible light is not accompanied by increase in mutations. One of the possible explanations is that the genotoxic effect due to damage of hemH, shortage of heme and/or accumulating of protoporphyrin IX makes mutagenesis impossible.
authors.affiliation: Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawińskiego 5A, 02-106 Warsaw, Poland.
authors.forename: Anna
authors.initials: A
authors.lastname: Sikora
authors.forename: Elzbieta
authors.initials: E
authors.lastname: Grzesiuk
authors.forename: Renata
authors.initials: R
authors.lastname: Zbieć
authors.forename: Celina
authors.initials: C
authors.lastname: Janion
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D004260:DNA Repair / Q000235:genetics* / Q000502:physiology; D004720:Endonucleases; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics*; D005294:Ferrochelatase / Q000235:genetics* / Q000378:metabolism; D008027:Light; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011524:Protoporphyrins / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D011524:Protoporphyrins; C028025:protoporphyrin IX; D004720:Endonucleases; D005294:Ferrochelatase