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J K Setlow

Publications and source records attributed to J K Setlow.

At least 73 records · Page 4Linked to original sources
PubMed1972

Repair of pyrimidine dimer damage induced in yeast by ultraviolet light.

Crude extracts from ultraviolet (UV)-irradiated yeast cells compete with UV-irradiated transforming deoxyribonucleic acid (DNA) for photoreactivating enzyme. The amount of competition is taken as a measure of the level of cyclobutyl pyrimidine dimers in the yeast DNA. A calibration of the competition using UV-irradiated calf thymus DNA indicates that an incident UV dose (1,500 ergs/mm(2)) yielding 1% survivors of wild-type cells produces between 2.5 x 10(4) to 5 x 10(4) dimers per cell. Wild-type cells irradiated in the exponential phase of growth remove or alter more than 90% of the dimers within 220 min after irradiation. Pyrimidine dimers induced in stationary-phase wild-type cells appear to remain in the DNA; however, with incubation, they become less photoreactivable in vivo, although remaining photoreactivable in vitro. In contrast, exponentially growing or stationary-phase UV-sensitive cells (rad2-17) show almost no detectable alteration of dimers. We conclude that the UV-sensitive cells lack an early step in the repair of UV-induced pyrimidine dimers.

Animals↗
PubMed1972

Molecular basis for the transformation defects in mutants of Haemophilus influenzae.

To determine the molecular basis of transformation defects in Haemophilus influenzae, the fate of genetically marked, (32)P-labeled, heavy deoxyribonucleic acid (DNA) was examined in three mutant strains (rec(1) (-), rec(2) (-), and KB6) and in wild type having (3)H-labeled DNA and a second genetic marker. Transforming cells upon lysis with digitonin followed by low-speed centrifugation are separable into the supernatant fraction, containing mainly the unintegrated donor DNA, and the pellet, containing most of the resident DNA along with integrated donor DNA. Electron micrographs of digitonin-treated cells also indicate that the resident DNA is trapped inside a cellular structure but that cytoplasmic elements such as ribosomes are extensively released. DNA synthesis in digitonin-treated cells is immediately blocked, as is any further integration of donor DNA into the resident genome. Isopycnic and sedimentation analysis of supernatant fluids and pellets revealed that in strains rec(2) (-) and KB6 there is little or no association between donor and resident DNA, and thus there is negligible transfer of donor DNA genetic information. In these strains, the donor DNA is not broken into pieces of lower molecular weight as it is in strain rec(1) (-) and in the wild type, both of which show association between donor and recipient DNA. In strain rec(1) (-), although some donor DNA atoms become covalently linked to resident DNA, the incorporated material does not have the donor DNA transforming activity.

Bacteriolysis↗
PubMed1972

Postreplication repair of ultraviolet damage in Haemophilus influenzae.

The deoxyribonucleic acid (DNA) synthesized following ultraviolet (UV) irradiation of wild-type (Rd) and recombination-defective strains of Haemophilus influenzae has been analyzed by alkaline sucrose gradient sedimentation. Strain Rd and a UV-resistant, recombination-defective strain Rd(DB117) (rec-) are able to carry out postreplication repair, i.e., close the single-strand gaps in the newly synthesized DNA; in the UV-sensitive, recombination-defective strain DB117, the gaps remain open. The lack of postreplication repair in this strain may be the result of degradation of the newly synthesized DNA.

Carbon Isotopes↗
PubMed1972

Mechanism of inactivation of Haemophilus influenzae transforming deoxyribonucleic acid by sonic radiation.

Transforming deoxyribonucleic acid (DNA) from Haemophilus influenzae was exposed to sonic radiation of various durations. Reductions in transforming ability of the DNA, cellular DNA uptake, and integration into the genome, and single- and double-stranded molecular weights of the transforming DNA were measured and compared. We conclude that (i) sonic radiation causes DNA strand breaks (almost always double-strand breaks with relatively few alkaline-labile bonds), the number increasing with exposure until the double-stranded molecular weight is reduced to less than 10(6) daltons; and (ii) since transformation is reduced about as much as integration and much more than uptake, inactivation of transforming DNA by sonic radiation appears to be caused mostly by failure of Haemophilus cells to integrate the transforming DNA that is taken into the cells. These results are similar to those for inactivation by X radiation but differ from those for ultraviolet radiation. A strand break caused by sonic radiation, however, does not necessarily inactivate the transforming DNA, whereas in the case of ionizing radiation it may. The results may be fit by the model proposed by Cato and Guild. From our data and the equation of Lacks, the minimum active site of DNA necessary for transformation and the frequency of exchanges between donor and recipient strands upon integration of transforming DNA were estimated as 0.35 x 10(6) to 0.7 x 10(6) daltons and 0.15 to 0.4 switches per 10(6) daltons, respectively.

Carbon Radioisotopes↗
PubMed1972

Molecular events accompanying the fixation of genetic information in Haemophilus heterospecific transformation.

Heterospecific transformation between Haemophilus influenzae and H. parainfluenzae was investigated by isopycnic analysis of deoxyribonucleic acid (DNA) extracts of (3)H-labeled transforming cells that had been exposed to (32)P-labeled, heavy transforming DNA. The density distribution of genetic markers from the resident DNA and from the donor DNA was determined by transformation assay of fractions from CsCl gradients, both species being used as recipients. About 50% of the (32)P atoms in H. parainfluenzae donor DNA taken up by H. influenzae cells were transferred to resident DNA, and only a small amount of the label was lost under conditions of little cell growth. There was less transfer in the reciprocal cross, and almost half of the donor label was lost. In both crosses, the transferred donor material transformed for the donor marker considerably more efficiently when assayed on the donor species than on the recipient species, indicating that at least some of the associated (32)P atoms are contained in relatively long stretches of donor DNA. When the transformed cultures were incubated under growth conditions, the donor marker associated with recipient DNA transformed the donor species with progressively decreasing efficiency. The data indicate that the low heterospecific transformation between H. influenzae and H. parainfluenzae may be due partly to events occurring before association of donor and resident DNA but results mostly from events that occur after the association of the two DNA preparations.

Bacteriolysis↗
PubMed1971

Mechanism of inactivation of transforming deoxyribonucleic acid by X rays.

Transforming deoxyribonucleic acid (DNA) from Haemophilus influenzae was exposed to X rays either in phosphate buffer or in 10% yeast extract. Relations between determinations of biological inactivation, DNA uptake by competent H. influenzae, integration of DNA into the competent cell genome, and induced single-and double-strand breaks indicate that transforming DNA is inactivated by the direct and the indirect effect of X radiation primarily because integration of DNA is prevented as a result of the production of double-strand breaks.

Buffers↗
PubMed1970

Ultraviolet-induced decrease in integration of Haemophilus influenzae transforming deoxyribonucleic acid in sensitive and resistant cells.

The decrease in integration of transforming deoxyribonucleic acid (DNA) caused by ultraviolet irradiation of the DNA was found to be independent of the presence or absence of excision repair in the recipient cell. Much of the ultraviolet-induced inhibition of integration resulted from the presence in the transforming DNA of pyrimidine dimers, as judged by the photoreactivability of the inhibition with yeast photoreactivating enzyme. The inhibition of integration made only a small contribution to the inactivation of transforming ability of the DNA by ultraviolet radiation.

DNA, Bacterial↗
PubMed1970

Repair of ultraviolet-irradiated transforming deoxyribonucleic acid in Haemophilus influenzae.

Ultraviolet-sensitive and wild-type Haemophilus influenzae cells were exposed to irradiated and unirradiated transforming deoxyribonucleic acid (DNA) containing a marker which can be linked to another marker in the cells. Lysates were made after various times of incubation and assayed for transforming activity on an excisionless recipient. Repair can be noted as an increase in activity from the irradiated donor DNA after its linkage to the recipient DNA. No repair can be observed in a mutant which is unable to integrate transforming DNA. There is a little repair in another mutant which is unable to excise pyrimidine dimers. H. influenzae cells also repair nondimer damage, as judged by the increase in activity observed in lysates made with irradiated and maximally photoreactivated DNA.

DNA Replication↗
PubMed1970

Endonuclease from Micrococcus luteus which has activity toward ultraviolet-irradiated deoxyribonucleic acid: its action on transforming deoxyribonucleic acid.

An endonuclease purified from Micrococcus luteus makes single-strand breaks in ultraviolet (UV)-irradiated, native deoxyribonucleic acid (DNA). The purified endonuclease is able to reactivate UV-inactivated transforming DNA of Haemophilus influenzae, especially when the DNA is assayed on a UV-sensitive mutant of H. influenzae. After extensive endonuclease action, there is a loss of transforming DNA when assayed on both UV-sensitive and -resistant cells. The endonuclease does not affect unirradiated DNA. The results indicate that the endonuclease function is involved in the repair of biological damage resulting from UV irradiation and that the UV-sensitive mutant is deficient in this step. We interpret the data as indicating that the various steps in the repair of DNA must be well coordinated if repair is to be effective.

DNA, Bacterial↗
PubMed1970

Transformation between Haemophilus influenzae and Haemophilus parainfluenzae.

Heterospecific transformation between Haemophilus influenzae and H. parainfluenzae is from one to more than six orders of magnitude lower than homospecific transformation, depending on the marker assayed. However, the physical integration of deoxyribonucleic acid (DNA) in heterospecific compared with homospecific transformation is only slightly decreased. Measurement of integration of ultraviolet-irradiated heterospecific transforming DNA suggests that compared with homospecific DNA a longer piece of heterospecific transforming DNA must undergo pairing for integration to occur. Heterospecific transforming DNA behaves towards ultraviolet inactivation of biological activity as though it had undergone some previous inactivation. The efficiency of heterospecific transformation can be improved by light sonic treatment of the DNA or by the use of DNA containing markers which originated from the heterospecific recipient. The presence of an excision mechanism in the recipient cell does not affect killing or marker efficiency in heterospecific transformation. The data indicate that the low frequency of transformation between H. influenzae and H. parainfluenzae results mostly from lethality. It is proposed that integration of heterospecific transforming DNA results in alterations in the base sequence of the recipient genome which cannot be repaired. Transcription and translation of the altered DNA could result in synthesis of nonfunctional essential proteins.

DNA, Bacterial↗
PubMed1969

Ultraviolet inactivation and photoproducts of transforming DNA irradiated at low temperatures.

Solutions of Haemophilus influenzae transforming DNA were irradiated at temperatures ranging from 25 degrees C to - 196 degrees C. Temperature dependence of the formation of thymine-containing dimers was closely correlated with inactivation of transforming activity; in general, both dimerization and inactivation decreased with decreasing temperature. The fraction of nonphotoreactivable damage increased with increasing dose at low temperatures. The nonphotoreactivable spore-type photoproduct was formed at low temperatures with a maximum at - 100 degrees C, a temperature at which the nonphotoreactivable biological inactivation was also a maximum. Intrastrand cross-linking, like dimer formation, decreased with decreasing irradiation temperature.

Chromatography, Paper↗