SENSITIVITY OF <i>HemA</i> MUTANT <i>Escherichia coli</i> CELLS TO INACTIVATION BY NEAR‐UV LIGHT DEPENDS ON THE LEVEL OF SUPPLEMENTATION WITH δ‐AMINOLEVULINIC ACID

Tuveson, R. W.; Sammartano, Lauri J.

doi:10.1111/j.1751-1097.1986.tb05637.x

Cited by 32 publications

(20 citation statements)

References 25 publications

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“…These proteins appeared to be acting as endogenous photosensitizers. These results were consistent with recently published work showing that cytochromes may also be acting in this manner (43). Further evidence of the involvement of oxidative damage in NUV toxicity came from our demonstration of the involvement of the oxidative Other endogenous photosensitizers likely to be important in NUV toxicity include cytochromes (3).…”

Section: Discussionsupporting

confidence: 82%

Oxidative mechanisms of toxicity of low-intensity near-UV light in Salmonella typhimurium

Kramer¹,

Ames²

1987

J Bacteriol

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The exposure of Salmonella typhimurium to environmentally relevant near-UV light stress has been studied by the use of a low-intensity, broad-band light source. The exposure of cells to such a light source rapidly induced a growth delay; after continuous exposure for 3 to 4 h, cells began to die at a rapid rate. The oxidative defense regulon controlled by the oxyR gene was involved in protecting cells from being killed by near-UV light. This killing may be potentiated by the overexpression of near-UV-absorbing proteins. These results are consistent with near-UV toxicity involving the absorption of light by endogenous photosensitizers, leading to the production of active oxygen species. We have shown, however, that one such species, H2O2, is not a major photoproduct involved in killing by near-UV light. Strains lacking alkyl hydroperoxide reductase were more sensitive to near-UV light, indicating that such hydroperoxides may be photoproducts. Near-UV exposure induced sensitivity to high salt levels, indicating that membranes may be a target of near-UV toxicity and a possible source of alkyl hydroperoxides. The demonstration of the inactivation of the heme-containing protein catalase indicates that direct destruction of UV-absorbing macromolecules could be another factor in near-UV toxicity. Cells which have been exposed to near-UV light for long, but sublethal, periods of time (up to 4 h) can recover and resume growth if the UV exposure is stopped but become progressively more sensitive to further stresses, such as H2O2. This result indicates that cells gradually accumulated damage during near-UV exposure until toxic levels were reached.

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Section: Discussionsupporting

confidence: 82%

Oxidative mechanisms of toxicity of low-intensity near-UV light in Salmonella typhimurium

Kramer¹,

Ames²

1987

J Bacteriol

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“…The major photosensitizers to near-UV killing in E. coli seem to be porphyrins, and mutations that cause porphyrin accumulation lead to near-UV sensitivity (25). We have no explanation for the increased sensitivity of A(attXuvrB) mutants to near-UV radiation except to note that these deletions eliminate the pterin-molybdenum cofactor (chiA) of nitrate reductase.…”

Section: Resultsmentioning

confidence: 99%

“…However, the twofold increase in sensitivity of A(gal-uvrB) strains compated with A(attXuvrB) strains may be explained as follows: the deletion of the hemF gene which is located in the gal-attX interval (1) eliminates the hemF gene product coproporphyrinogen III oxidase and thus leads to accumulation of coproporphyrin in the cell, which in turn photosensitizes to near-UV killing. This hypothesis can be tested by combining this mutation with other mutations in genes controlling the earlier steps of porphyrin biosynthesis (25).…”

Section: Resultsmentioning

confidence: 99%

Photoreactivation in phr mutants of Escherichia coli K-12

Husain¹,

Sancar

1987

J Bacteriol

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We have investigated the genetics of photoreactivation in Escherichia coli K-12. We found that strains with point mutations or deletions in the phr gene showed a significant residual level of photoreactivation after exposure to large fluences of photoreactivating light. It had been previously proposed that a gene in the gal-attX interval is also involved in photoreactivation and that the residual photoreactivating activity might be due to this so-called phrA gene located at this interval. We found that deletions of the gal-attA region had no effect on either the rate or the final extent of photoreactivation observed in phr+ cells or phr mutants; however strains carrying the A(gal-attf) deletions displayed increased sensitivity to near-UV radiation.Photoreactivation has been defined as the reversal of the effects of far-UV (200-to 300-nm) radiation by subsequent exposure of cells to longer-wavelength light (300 to 600 nm) (7). That the major component of photoreactivation is enzymatic in Escherichia coli was established in 1958 (14), and the first phr mutant was isolated in 1962 (3). This mutation was isolated in E. coli B and subsequently mapped near gal in an E. coli K-12-E. coli B hybrid. (28). Later, it was reported that in E. coli K-12 cells with A(gal-attX), no photoreactivation could be detected, and therefore it was concluded that the gene for photoreactivation, phr, was located in this interval. A Adgal lysogen overproduced a 40-kilodalton (kDa) glycoribonucleoprotein which had photoreactivation activity (21, 22). However, further investigation of the A(gal-attX) mutants showed that these cells were capable of photoreactivating UV damage to the same extent as wild-type cells and that the phr gene was located outside the gal-attA interval, 1 min counterclockwise to gal, between kdp and gltA, and at 16.2 min on the recalibrated E. coli linkage map (1,15,29). The protein encoded by this gene was found to encode a 54-kDa flavoprotein which had in vitro photoreactivation activity comparable to the in vivo rate (17,18). To resolve the controversy, Sutherland and Hausrath (23) investigated the photoreactivation kinetics in wild-type and A(gal-attX) strains and reported that whereas the A(gal-attX) strains could indeed be photoreactivated, the rate of photoreactivation was much slower in strains with this deletion; they suggested that there were two genes controlling photoreactivation in E. coli, one at the gal-attX interval and one at the kdp-gltA interval, and proposed the designations phrA and phrB, respectively, for these loci. More recently it has been suggested (24) that the phrA gene encodes a 40-kDa protein that has an RNA cofactor (21), while the phrB gene encodes the 54-kDa photolyase that has a flavin adenine dinucleotide cofactor (17). However, the presence of two photoreactivating enzymes is inconsistent with other genetic data indicating that Harm's phr (phrB) mutant cannot be photoreactivated (2, 3), as well as with biochemical data showing the lack of dimer splitting by cell extracts from this st...

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“…Macromolecules which absorb in the near-UV region (i.e., heme and flavins) may act as endogenous photosensitizers, transferring the absorbed energy to 02 and forming toxic oxygen species (10,22,23,48). The response of bacteria to oxidative stress (such as H202) includes inhibition of growth and the induction of proteins involved in defense against the stress (11,12,30).…”

mentioning

confidence: 99%

Near-UV stress in Salmonella typhimurium: 4-thiouridine in tRNA, ppGpp, and ApppGpp as components of an adaptive response

1988

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We have examined the role of 4-thiouridine in the responses of Salmonella typhimurium to near-UV irradiation. Mutants lacking 4-thiouridine (nuv) and mutants defective in the synthesis of ppGpp (guanosine 5'-diphosphate-3'-diphosphate) (relA) were found to be sensitive to killing by near-UV. Near-UV induced the synthesis of a set of proteins that were not induced in the nuv mutant. Some of these proteins were identified as oxidative defense proteins, and others were identified as ppGpp-inducible proteins. Over 100-fold increases in ApppGpp (adenosine 5', 5"'-triphosphoguanosine-3"'-diphosphate, the adenylylated form of ppGpp) were observed in wild-type cells after near-UV irradiation but not in the 4-thiouridine-deficient mutant. These data support a model in which ppGpp and ApppGpp, a dinucleotide proposed to be synthesized by tRNA-aminoacyl synthetases as a response to the cross-linking of 4-thiouridine in tRNA by near-UV, induce the synthesis of proteins necessary for resistance to near-UV irradiation.One of the most common stresses confronted by organisms is solar radiation. The most energetic part of the solar spectrum which penetrates the atmosphere is the near-UV region (300 to 400 nm) (22). Studies on the environment mortality of bacteria have found that die-off is dependent on light exposure, especially the near-UV portion of the solar spectrum (10,16,17). Since enteric bacteria such as Escherichia coli must adapt to exposures of near-UV during transmission between hosts (8), they are an ideal system for characterizing mechanisms involved in protection from the toxic effects of near-UV.The irradiation of growing E. coli cells with near-UV results in the cessation of growth long before lethal effects are observed (21,22). This growth lag is dependent on the tRNA-modified base 4-thiouridine (s4U), which is found in 65% of tRNA species (22,40,45). This base is unusual in that it has an absorption maximum in the near-UV region (334 nm). After exposure to near-UV, S4U participates in a photochemical reaction which generates intramolecular cross-linking between S4U and a specific cytosine (13,14,29). These cross-linked tRNAs have been shown to be poor substrates for aminoacylation (51). The accumulation of nonaminoacylated tRNA serves to trigger the stringent response via the relA gene product, which is involved in the synthesis of ppGpp (guanosine 5'-diphosphate-3'-diphosphate) (9, 15), which then acts to inhibit stable RNA synthesis while inducing amino acid biosynthesis (15, 43). Inhibition of protein synthesis after near-UV exposure in E. coli is a result of both the stringent response and decreased aminoacylation of tRNA (44).Near-UV exerts toxic effects on E. coli and Salmonella typhimurium at higher fluences, primarily through oxidative mechanisms (22, 23). Macromolecules which absorb in the near-UV region (i.e., heme and flavins) may act as endogenous photosensitizers, transferring the absorbed energy to 02 and forming toxic oxygen species (10,22,23,48). The response of bacteria to oxidative stress (s...

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SENSITIVITY OF HemA MUTANT Escherichia coli CELLS TO INACTIVATION BY NEAR‐UV LIGHT DEPENDS ON THE LEVEL OF SUPPLEMENTATION WITH δ‐AMINOLEVULINIC ACID

Cited by 32 publications

References 25 publications

Oxidative mechanisms of toxicity of low-intensity near-UV light in Salmonella typhimurium

Oxidative mechanisms of toxicity of low-intensity near-UV light in Salmonella typhimurium

Photoreactivation in phr mutants of Escherichia coli K-12

Near-UV stress in Salmonella typhimurium: 4-thiouridine in tRNA, ppGpp, and ApppGpp as components of an adaptive response

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