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Biomedical subjects

M W Lieberman

Publications and source records attributed to M W Lieberman.

14 recordsLinked to original sources
PubMed1979

Distribution of DNA damage in chromatin and its relation to repair in human cells treated with 7-bromomethylbenz(a) anthracene.

We have examined the relationship between the distribution of DNA damage and repair in chromatin from confluent human fibroblasts treated with the carcinogen 7-bromomethylbenz (a) anthracene. Analysis of staphylococcal nuclease (SN)4 digestion kinetics and gel electrophoresis revealed that more total damage occurs in nucleosome core DNA (approximately 80-85% of chromatin DNA) than in SN sensitive DNA (APPROXIMATELY15-20%). Furthermore, over a 24 hr period, damage is removed at about the same rate from these two regions. In contrast, virtually all of the nucleotides incorporated during repair synthesis are initially SN sensitive even when measured at 12 hr after damage. With time many repair-incorporated nucleotides become SN resistant and coelectrophorese with nucleosome core DNA. To explain these data we propose a model whereby excision repair occurs in both linker and core DNA; however, in core DNA the repair process induces conformational changes resulting in temporarily increased SN sensitivity; subsequently, rearrangement occurs and results in the re-establishment of native or near-native nucleosome conformation and SN resistance.

Benz(a)Anthracenes↗
PubMed1978

Nucleosome rearrangement in human chromatin during UV-induced DNA- reapir synthesis.

The distribution of UV-induced DNA repair synthesis within chromatin was measured in confluent human fibroblasts that were pulse-labeled with [3H]dThd (10 or 90 min) immediately after irradiation and chased in nonradioactive medium for different time periods. Initially (i.e., at the end of the pulse period), most of the repair synthesis occurs in staphylococcal nuclease-sensitive regions. With increasing chase times the nucleotides inserted during repair synthesis become progressively more nuclease resistant. Gel electrophoresis data indicate that nuclease resistance is conferred on these nucleotides by their appearance in core DNA. The kinetics of this rearrangement process are biphasic: greater than 85% of the repair synthesis sites undergo rapid rearrangement (4--5 hr); the remaining sites ( less than 15%) rearrange much more slowly, if at all. The time courses of nucleosome rearrangement and repair synthesis are similar, suggesting that nucleosome rearrangement may be induced by the repair process or that the rate of repair synthesis may be regulated by nucleosome rearrangement.

Cell Cycle↗
PubMed1978

The distribution of DNA repair synthesis in chromatin and its rearrangement following damage with N-acetoxy-2-acetylaminofluorene.

The distribution of DNA repair synthesis in the chromatin of confluent human diploid fibroblasts damaged with N-acetoxy-2-acetylaminofluorene has been studied. Kinetic analysis of staphylococcal nuclease digestion data revealed that initially most of the repair synthesis occurred in nuclease sensitive regions of chromatin. Continuous labeling experiments and pulse chase experiments indicated that with time much of the 3H dThd initially incorporated into nuclease sensitive regions during repair appeared in nuclease resistant regions. Agarose gel electrophoresis was used to demonstrate that these resistant regions were core DNA. In agreement with previous findings [Smerdon, M.J. and Lieberman, M.W., (1978), Proc. Nat. Acad. Sci. USA, in press], studies of the time course of this rearrangement and of repair synthesis revealed similar time dependences and suggested a relationship between rates of repair synthesis and chromatin rearrangement.

Acetoxyacetylaminofluorene↗
PubMed1977

Adduct formation between the carcinogen N-acetoxy-2-acetylaminofluorene and synthetic polydeoxyribonucleotides.

The chemical carcinogen N-acetoxy-2-acetylaminofluorene (NA-AAF) was reacted with poly(dG-dC) - poly(dG-dC); poly dG - poly dC; poly(dA-dT) - poly (dA-dT); and poly dA - poly dT under a variety of conditions. Poly (dG-homo GC polymer and 10--20 more reactive the A + T polymers. Lowering the ionic strength increased the extent of reaction, while pH change (8.9 vs. 5.5) had only a small effect. If ionic strength was adjusted so that the two guanine-containing polymers showed equal thermal stability (as judged by Tm) then the alternating copolymer was 7 times as reactive as the homopolymer. In aggreement with previous investigators, the major product was found to be 8-(N-2-fluorenylacetamido) deoxyguanosine.

Acetoxyacetylaminofluorene↗
PubMed1977

Interaction of cis- and trans-dichlorodiammine-platinum(II) with synthetic polydeoxyribonucleotides: effect of equilibrium buoyant densities.

Equilibrium buoyant densities in CS2SO4 of four synthetic double-stranded polydeoxyribonucleotides were compared following reaction with either cis-Pt(NH3)2Cl2, trans-Pt(NH3)2Cl2 or PtCl4. While both Pt(NH3)2Cl2 isomers caused significant increases in the buoyant densities (rho) of the two G + C polymers, the cis- isomer increased the rho of poly [d(G-C)] and the trans- isomer increased the rho of poly(dG) - poly(dC) more sharply than the corresponding isomer at low molar ratios of metal ion to polymer. Chloroplatinic acid was without effect. Only cis-Pt(NH3)2Cl2 produced substantial increases in the rho of poly[d(A-T)] and poly(dA) - poly(dT) with increasing metal ion concentrations. These increases were accompanied by a proportional decrease in the thermal transition temperature (Tm) of poly(dA)-poly(dT) and a sharp increase in the Tm of poly[d(A-T)]. Our results indicate that the cis- isomer reacts with all four polymers to produce rho changes clearly distinct from those values observed after reaction with either the trans- isomer or PtCl4. These results help explain the observation by others that the cis- isomer produces greater rho changes in native DNA than the trans- isomer. On the basis of our data and the published results of others, one may rationalize the quantitative differences between the cis- and trans-compounds of the buoyant densities of naturally occurring DNA; however, additional studies are clearly needed.

Binding Sites↗
PubMed1977

Differences in removal of acetylaminofluorene and pyrimidine dimers from the DNA of cultured mammalian cells.

The rate and extent of disappearance of two DNA lesions (pyrimidine dimers and covalently bound acetylaminofluorene), both thought to be removed by the so-called wide-patch (approximately 100 nucleotides) repair process, were studied in a variety of cultured mammalian cells. With the exception of mouse cells, dimers were removed more rapidly and extensively than covalently bound acetylaminofluorene. In human cells, for example, about 50% of the dimers were excised from DNA in 1 hr while only 25-50% of the chemically induced lesions were excised from DNA after 48 hr. Surprisingly mouse cells, which remove few dimers, were about as competent as control human fibroblasts at removing acetylaminofluorene lesions; however, xeroderma pigmentosum cells (group D) removed fewer N-acetoxy-2-acetylaminofluorene-induced lesions than control human cells. Our data raise the possibility of separate repair processes for these two types of lesions and suggest that their expression may be under similar genetic control in human cells.

2-Acetylaminofluorene↗
PubMed1977

Levels of DNA polymerases alpha, beta, and gamma in control and repair-deficient human diploid fibroblasts 1.

The activities of DNA polymerases alpha, beta, and gamma were determined in control and repair-deficient human fibroblasts (xeroderma pigmentosum complementation groups A, C, and D; Fanconi's Anemia; and Bloom's syndrome). Assays were done on 103,000XG supernatants which had been chromatographed on DEAE cellulose to remove nucleic acids and on fractions containing polymerase activities which had been separated from one another on a second DEAE cellulose column. All repair-deficient cell types contained all three DNA polymerase activities. Caffeine, which has been observed to inhibit some DNA-repair processes in intact cells, had no effect on DNA polymerase activities from XP-A, XP-C, XP-D or XP-variant cells. These data indicate that all three polymerases are present in cells which have reduced or absent repair functions and that the caffeine effects observed in living cells are probably not due to the direct action of caffeine on DNA polymerases.

Anemia, Aplastic↗