Photoreversal-dependent release of thymidine and thymidine monophosphate from pyrimidine dimer-containing DNA excision fragments isolated from ultraviolet-damaged human fibroblasts

To elucidate the enzymatic excision-repair process operative on cyclobutane-type pyrimidine photodimers in human dermal fibroblasts, we have examined excised dimer-containing material recovered in the trichloroacetic acid soluble fraction from far-ultraviolet-irradiated (254 nm, 40 J m-2) and incubated (24 h) cell cultures. The excised DNA photoproducts were found in oligonucleotide fragments with an estimated mean chain length of approximately 3.7 bases. Exposure of these isolated excision fragments, labeled with [3H]thymidine (dT), to a secondary, dimer-photoreversing fluence of far-UV (5.5 kJ m-2) resulted in the release of free dT and thymidine monophosphate (TMP). Photorelease of these two radioactive species was measured by high-performance liquid chromatography, with TMP being detected as the increase in dT following bacterial alkaline phosphatase treatment. These data imply that the photoliberated dT and TMP moieties were attached to the excision fragments solely by the cyclobutane ring of the dimer. No evidence was obtained for the photoliberation of free thymine, thus corroborating a conclusion reached by others that the excision of dimers in human cells is not initiated by scission of an intradimer N-glycosyl bond. The sum of the tritium label recovered in dT plus TMP corresponded to approximately 40% of that disappearing from thymine-containing dimers on photoreversal, suggesting that in about 80% of the isolated excision fragments the dimer is located at one end of the oligonucleotide and contains a break in its internal phosphodiester bond.(ABSTRACT TRUNCATED AT 250 WORDS)

Stereospecific removal of methyl phosphotriesters from DNA by an Escherichia coli ada+ extract

The ada+ gene product, a DNA methyltransferase present in extracts from an Escherichia coli strain constitutive for the adaptive response, removes only half of the methyl phosphotriesters from alkylated DNA. Since DNA phosphotriesters occur in two isomeric configurations (denoted Rp and Sp), we examined whether this reflects a stereospecific mode of repair by the methyltransferase. Analysis by reverse-phase HPLC, phosphorus NMR and circular dichroism established that only triesters in the Sp configuration are acted upon by the E. coli extract.

Stability of coping style 33 years after prolonged exposure to extreme stress

Respondents who were in hiding or in the armed resistance movement in Nazi occupied Europe are assumed to have had avoidant and confronting coping styles, respectively. Responses to questionnaire items tapping behavior, attitudes and perceptions were examined in the two groups for the persistence of these same traits 33 years after World War II, in a study of randomly selected community sample of Jews. Taken as a whole, but not individually, responses to the questionnaire items suggested that the traits did persist (P less than 0.001). The results highlight the importance of distinguishing individual differences in coping style when studying the long-term effects of prolonged, stressful experiences.

Impairment in Holocaust survivors after 33 years: data from an unbiased community sample

The authors compared the psychiatric status of 135 survivors of the Holocaust with that of control subjects. This study stands apart from most previous reports in that the two groups were generated by a random sample survey of all heads of households in a community (Montreal). Survivors were more likely to have mild psychiatric symptoms regardless of the age at which they experienced the Holocaust. The difference between survivors and controls in levels of mild psychiatric symptoms was greatly amplified in those respondents who perceived a recent increase in anti-Semitism in Montreal.