Frequency Of UV-induced Mutations Research Articles

The effect of post-treatment with caffeine on survival and UV-induced mutation frequencies in chinese hamster and mouse lymphoma cells in vitro

The effect of post-treatment with caffeine on the survival of a number of cell lines after UV-irradiation has been studied. The mouse lymphoma cell lines P388 and L5178YS were sensitized by caffeine but only after UV doses of 50 erg/mm 2 and above. V79 cells also showed sensitization by caffeine but CHO cells and two cell lines YS and YR derived from Yoshida sarcoma of rats, sensitive and resistant to UV radiation, respectively, showed no effect. P388 and V79 cells were both mutable by UV, and caffeine, when studied at a single expression time (42–48 h) and at a single dose level (0.5 M and 0.75 M, respectively) suppressed the UV-induced mutation frequency in both cell lines. L51788YS cells although sensitized by caffeine showed no increase in frequency of thymidine-resistant (TdR r) colonies when irradiated with UV. On more detaled examination, caffeine was found to delay the expression of UV-induced mutations inV79 cells, and the delay was dependent on the dose of caffine used. The effect on expression time was less when caffeine was present 0–48 h than when it was present throughout the post-irradiation incubation period. Similar results were obtained in P388 cells. The data are discussed in relation to those of other workers and to the concept that caffeine inhibits an error prone post-replication repair process in mammalian cells

Inhibition of repair of UV-damaged DNA by caffeine and mutation induction in Chinese hamster cells

The effect of caffeine on UV-irradiated Chinese hamster cells in vitro was studied on the cellular and molecular levels. Caffeine (1 m M) was shown to decrease the colony-forming ability and the frequencies of spontaneous and UV-induced mutations in Chinese hamster cells. The effect of caffeine in reducing the frequency of UV-induced mutations was demonstrated only if caffeine was present in the culture medium during the first post-irradiation cell division. Using alkaline sucrose gradient centrifugation, both parental and newly synthesized DNA in UV-irradiated and unirradiated cells were studied in the presence and absence of caffeine. Caffeine affected the sedimentation profile of DNA synthesized in UV-irradiated cells but not in unirradiated cells. Caffeine had no apparent effect on the incorporation of [ 3H]-thymidine into DNA of control or UV-irradiated cells, nor on the small amount of excision of UV-induced pyrimidine dimers. These results may be interpreted by a hypothesis that caffeine inhibits a certain S-phase specific, post-replication, dark-repair mechanism. The hamster and perhaps other rodent cells exposed to low doses of UV are capable of DNA replication, by-passing the non-excised pyrimidine dimers. This postulated repair process probably involves de novo DNA synthesis to seal the gaps in the nascent strand. This repair may be also responsible for the enzymatic production of mutations.

Ultraviolet mutagenesis in repair-deficient derivatives of Escherichia coli B/r: uvrA uvrB and uvrA recC strains

UV mutability of uvrA derivatives of E. coli B/r carrying recB or recC mutations was compared with that of otherwise isogenic Rec + strains. The frequency of UV-induced mutations per survivor from Try − to Try + and from Str-s to Str-r, as well as the absolute yields of these mutations, was significantly lower in the recB and recC strains thatn in Rec + at the same UV doses. The results support the hypothesis that UV-induced mutations in these strains originate as errors associated with the occurrence of recA +-dependent post-replication repair of gaps in DNA opposite pyrimidine dimers, and that maximal UV mutability requires participation of the recB- recC nuclease in this repair process. The reduced mutability of recB and recC strains may reflect a change in the accuracy of post-replication repair, such that fewer errors are made per gap repaired than in Rec + strains. Alternatively, the accuracy of post-replication repair may be unchanged, and the reduced UV mutability may result from the reduced tolerance of recB and recC strains for exercised pyrimidine dimers, with consequent selective survival of a fraction of the irradiated poplation containing fewer dimers per cell, compared to the surviving fraction in Rec + at the same UV dose. Data obtained at very low doses of UV indicate that reduced dimer tolerance alone cannot account for the observed reduction in UV mutability of recB and recC strains, unless it is assumed that dimer tolerance is not equally reduced in different regions of the genome.

Defective excision repair of pyrimidine dimers in the ultraviolet-sensitive Escherichia coli ras- mutant.

The ras(-) mutant of Escherichia coli K-12 is sensitive to ultraviolet (UV) light but only slightly sensitive to X-irradiation (1.5-fold increase). Other phenotypic properties include normal recombination ability and normal host cell reactivation ability but an abnormally high frequency of UV-induced mutation. The response of the ras(-) mutant to UV has been studied biochemically. After low doses of UV, the ras(-) mutant degraded excessive amounts of deoxyribonucleic acid, and long delays in resumption of deoxyribonucleic acid synthesis occurred. Pyrimidine dimers were excised at the normal rate. Although the mutant had the capability of initiating repair replication, the process was not completed after the high UV dose required to allow detection of repair replication. The ras(-) mutant, after low UV doses, left three to four times as many single-strand breaks not rejoined as did the wild-type strain.

Escherichia coli ras locus: its involvement in radiation repair.

There are several classes of Escherichia coli mutants defective in radiation repair. These include strains defective in pyrimidine dimer excision, in photoreactivation, in recombination, in repair of X-ray damage, and ultraviolet (UV)-conditional mutants which do not divide after UV. Another mutant (ras(-)) has been isolated. The ras(-) has increased UV sensitivity, but only slightly increased X-ray sensitivity (1.5-fold increase). Ability to effect genetic recombination, to reactivate irradiated bacteriophage T1, and to be photoreactivated is normal. UV-induced mutation frequency is greatly increased in the mutant. The ras(-) apparently lacks the ability to repair some UV damage in the bacterial cell but can repair UV damage to bacteriophage DNA. The ras locus is located between lac and purE on the chromosome map.

Recovery from the mutagenic effect of ultraviolet irradiation in Ophiostoma.

Abstract When cells from two auxotrophic mutants of Ophiostoma multiannulatum are irradiated with UV light the frequency of revertants to wild type decreases if the cells are incubated in liquid medium following UV irradiation. The decrease is dependent on an enzymatic process, energy requiring and temperature dependent, and ceases when the cells are starved of nitrogen or glucose or treated with sodium azide. The decrease in mutation frequency also stops when the cells are plated by mixing them with the agar substrate. The cells exude into the liquid medium compounds with nucleic acid absorption, and these compounds induce reversions in a hypoxanthine-less strain. The results are discussed and compared with similar observations on modification of UV-induced mutation frequency and lethality in bacteria.

Photoreversion und Photoprotektion bei UV-induzierten Mutationen des nichtphotoreaktivierbaren Bacteriums E.coli phr−

Stationary phase cells of strain phr−/MC 2 ofE. coli are not photoreactivable but the frequency of UV-induced mutations to low Streptomycine-resistance („S 3”, 3γ/ml) is decreased strongly by illumination with „light” of fluorescence tubes (310 to 500 nm) after UV-irradiation. Also dark-reversion (DRM) of these mutations due to keeping UV-irradiated cells in saline is observed. Illumination before UV-irradiation decreases the frequency of the mutations (photoprotection against mutation=PPM) to the same extent as the combined action of photoreversion (PRM) and DRM. The lag-phase of cell division is prolonged strongly by illumination from 80 min without “light” to 150 min by the “light”-dose of highest activity. The additional lag is nearly the same if the illumination is done before, after or without UV-irradiation; this lag is about additive to the small lag caused by UV. Pre-illumination of the stationary-phase cells does not cause photoprotection against killing (PP), it even decreases the survival after high UV-doses. The observations support the hypothesis that PRM in this strain may be “indirect”, i.e. caused by the “light”-induced additional division lag which enhances the dark repair of UV-premutations. Also spontaneous premutations which are apparently present in the stationary-phase cells seem to be influenced by the “light” in this way.