Knowledge of Pap screening and human papillomavirus among women attending clinics in Medellín, Colombia

This study evaluated Pap screening and human papillomavirus (HPV) knowledge in a population of Colombian women as a possible contributing factor of low cervical cancer screening success. This is a descriptive, cross-sectional analysis of 454 women who were approached in five different hospitals and clinics throughout Medellín, Colombia. Of them, 449 females agreed to participate and answered a standardized face-to-face questionnaire regarding Pap screening and HPV knowledge. Using logistic regression, predictors of both Pap and HPV knowledge were examined. Overall, 76.3% of the participants exhibited a high level of Pap screening knowledge, while only 7.8% showed high level of HPV knowledge. Of the 449 women, 71.5% reported that it had been 1 year or less since their last Pap test, while 7.8% reported never having had a Pap test or not having had a recent test. Factors influencing Pap screening knowledge included education level and insurance; factors influencing HPV knowledge included education level and age. The high level of Pap screening knowledge and use do not explain the high cervical cancer rates in Colombia. The results of this study suggest that educational efforts should be focused on increasing women's knowledge and awareness of HPV in anticipation of the availability of HPV vaccines and HPV tests for screening

Lack of evidence for local immune activity in oral hairy leukoplakia and oral wart lesions

BACKGROUND

Oral warts, caused by human papillomavirus (HPV), and oral hairy leukoplakia (OHL) caused by Epstein-Barr virus (EBV), are common oral manifestations in HIV-infected persons. Although both conditions occur most often with reduced blood CD4+ T-cell numbers, oral warts and OHL rarely occur simultaneously, suggesting that dysfunctions in other secondary local immune parameters are also involved. The present study evaluated tissue-associated proinflammatory and T-helper cytokine and chemokine mRNA expression and the presence of T cells in each lesion.

METHODS

Biopsies were taken from lesion-positive and adjacent lesion-negative sites of HIV+ persons with oral warts or OHL and lesion-negative sites from HIV+ persons who were oral HPV or EBV DNA-positive (matched controls). Cytokine/chemokine mRNA expression was quantified by real-time polymerase chain reaction. CD3, CD4, and CD8 cells were identified by immunohistochemistry.

RESULTS

No differences were detected in tissue-associated cytokine/chemokine mRNA expression in warts or OHL when compared to lesion-negative sites. Immunohistochemical analysis of T cells showed CD8+ cells exclusively, but few cells were present in either lesion. No differences were detected between lesion-positive and -negative control sites of each pathologic condition.

CONCLUSION

Little evidence was found for local immune reactivity to either oral warts and OHL, suggesting that CD4+ T cells are a primary host defense against both oral warts and OHL, but with nonimmune factors potentially responsible for the divergent prevalence of each.

Comparative analysis of methods for collection and measurement of cytokines and immunoglobulins in cervical and vaginal secretions of HIV and HPV infected women

The goal of these studies was to distinguish which of two techniques [cervicovaginal lavage (CVL) and cervical wick (SS)] is the optimal collection method for the measurement of the local immunological response in human papillomavirus (HPV) and HIV infected women. The following parameters were measured in 24 paired samples from 15 women (9 HIV+, 6 HIV-): total protein, immunoglobulin levels, HPV-specific antibodies, and Th1-Th2 cytokines. In addition, relative mRNA levels from CVL cell pellets were compared to protein levels from CVL supernatants. The total protein (2-fold) and IgG concentration (10-fold) are higher in the SS samples, were reproducible (%CV<3) and these levels correlated (P<0.0001) with their paired CVL sample. Type-specific HPV-L1 IgG and IgA antibodies were detected in CVL and SS (r>0.28, P<0.008) with excellent reproducibility (CV<3.0%). However, SS (%CV>18) failed to yield reproducible results for the cytokine assays as compared to the CVL (%CV<5.0). Furthermore, no correlations were found between relative mRNA levels from CVL cell pellet and cytokine protein levels in CVL supernatants. The CVL sample's superior reproducibility in the cytokine assays makes this the better collection method. In addition, cytokine protein level's failure to correlate with mRNA suggests tight regulation of cytokine genes or production from a different cell population.

Seroepidemiology of low and high oncogenic risk types of human papillomavirus in a predominantly male cohort of STD clinic patients

Human papillomaviruses (HPV) infecting the genital tract are associated with warts and anogenital malignancies. Although HPV is a highly prevalent sexually transmitted disease (STD), the majority of research has focused on female cohorts due to gender specific sequelae. Our objective was to measure the epidemiological features and seroprevalences of HPV-6/11 and 16 in a predominantly male group of STD clinic patients. High-risk individuals (n=687), who attended the public STD clinic were administered a behavioural questionnaire and serum tested for antibodies against HPV-6/11 and HPV-16 capsids via capture enzyme-linked immunosorbent assay. Despite the male predominance in this study, women were significantly more likely to have antibodies against both HPV-6/11 and HPV-16. Condom use appeared to be partially protective against HPV-16 seropositivity only. In conclusion, despite exhibiting increased risk behaviour, men were less likely to be HPV seropositive. Additional studies utilizing male cohorts are warranted to further elucidate this phenomenon.

Detection of cervical antibodies to human papillomavirus type 16 (HPV-16) capsid antigens in relation to detection of HPV-16 DNA and cervical lesions

A more sensitive luminescence immunoassay (LIA) for human papillomavirus type 16 (HPV-16) was developed and used to measure HPV-16 antibodies in cervical samples from 292 college-aged women who were examined at 4-month intervals. Of the 609 collected samples, IgG, IgA, and secretory piece-associated antibodies to HPV-16 were detected in 12%, 6%, and 8%, respectively, of samples tested. Cervical IgG antibodies were most strongly associated with HPV-16 DNA detected within the previous 12 months (odds ratio, 3.3; 95% confidence interval, 1.4-7.8). Secretory IgA (cervical IgA- and secretory piece-positive) was most strongly associated with detection of a squamous intraepithelial lesions 4-8 months earlier (odds ratio, 6.4; 95% confidence interval, 1.9-21.8). As with serum HPV-16 antibodies, there appears to be a several-month delay between cervical HPV infection and detection of cervical antibodies.

Infection with Human Papillomavirus: Update on Epidemiology, Diagnosis, and Treatment

Human papillomavirus (HPV) infection is the most common sexually transmitted viral disease worldwide. Low-risk types of HPV (eg, HPV-6 and HPV-11) are the causative agents of genital warts, whereas high-risk types (eg, HPV-16 and HPV-18) have been associated with anogenital cancer, particularly cervical cancer. Cervical cancer remains the second most common cancer in women worldwide. Recent advances have led to a better understanding of how HPV causes cancer on a molecular level and of the immunologic response to HPV. Methods to detect HPV infection have been improved, and a new treatment method for genital warts has been developed. The production of empty capsids of HPV done using recombinant technology has led to the development of serologic assays for HPV. The empty capsids are now the basis of clinical trials of vaccines to prevent HPV infection and disease.

Seroprevalence of human papillomavirus type 16 in pregnant women

OBJECTIVE

To determine the seroprevalence of and risk factors for human papillomavirus (HPV) type 16 capsid antibodies in a large cohort of pregnant women.

METHODS

Antibodies against in vitro produced HPV-16 capsids were measured in stored sera from 2597 pregnant women enrolled from 1984 through 1989 in the Vaginal Infection and Prematurity Study, New Orleans site.

RESULTS

Women in this study were primarily black (83.4%) with a mean age of 23.4 years (standard deviation [SD], 5.1), mean number of sexual partners in lifetime was 3.3 (SD, 6.6), and the mean age at sexual debut was 16.7 years (SD, 2.2). Overall, 28.0% (n = 727) of these women were positive for HPV-16 capsid antibodies. In bivariate analysis, the presence of antibodies against HPV-16 was correlated with numerous demographic characteristics as well as history of various sexually transmitted diseases. However, neither current cervical or vaginal infection nor adverse obstetric outcome was associated with increased detection of HPV-16 antibodies. In multivariate logistic regression analysis, factors predictive of HPV-16 seropositivity were: more than five lifetime sexual partners (odds ratio [OR], 1.80; 95% confidence interval [CI], 1.28, 2.52), 6 or more years of sexual activity (OR, 1.84; 95% CI, 1.22, 2.78), level of education (OR, 1.26; 95% CI, 1.03, 1.55), and history of Neisseria gonorrhoeae infection (OR, 1.53; 95% CI, 1.20, 1.96).

CONCLUSION

HPV-16 seropositivity correlates with measures of sexual activity, confirming its role as a sexually transmitted disease, and its prevalence is similar to that in nonpregnant populations. HPV-16 seropositivity does not predict an adverse obstetric outcome.

Cofactors with human papillomavirus in a population-based study of vulvar cancer

BACKGROUND

Human papillomavirus (HPV) has been previously associated with vulvar cancer. In a population-based study, we examined whether exposure to HPV, cigarette smoking, or herpes simplex virus 2 (HSV2) increases the risk of this cancer.

METHODS

Incident cases of in situ (n = 400) and invasive (n = 110) squamous cell vulvar cancer diagnosed among women living in the Seattle area from 1980 through 1994 were identified. Serum samples were analyzed for antibodies against specific HPV types and HSV2. HPV DNA in tumor tissue was detected by means of the polymerase chain reaction. In most analyses, case subjects were compared with population-based control subjects (n = 1403). Relative risks of developing vulvar cancer were estimated by use of adjusted odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Increased risks of in situ or invasive vulvar cancer were associated with HPV16 seropositivity (ORs = 3.6 [95% CI = 2.6-4.8] and 2.8 [95% CI = 1.7-4.7], respectively), current cigarette smoking (ORs = 6.4 [95% CI = 4.4-9.3] and 3.0 [95% CI = 1.7-5.3], respectively), and HSV2 seropositivity (ORs = 1.9 [95% CI = 1.4-2.6] and 1.5 [95% CI = 0.9-2.6], respectively). When the analysis was restricted to HPV16 DNA-positive tumors (in situ or invasive), the OR associated with HPV16 seropositivity was 4.5 (95% CI = 3.0-6.8). The OR for vulvar cancer was 18.8 (95% CI = 11.9-29.8) among current smokers who were HPV16 seropositive in comparison with never smokers who were HPV16 seronegative.

CONCLUSIONS

Current smoking, infection with HPV16, and infection with HSV2 are risk factors for vulvar cancer. Risk appears particularly strong among women who are both current smokers and HPV16 seropositive.

Seroprevalence of human papillomavirus types 6 and 16 capsid antibodies in homosexual men

Human papillomavirus (HPV) has been implicated in the pathogenesis of anal carcinoma, which is increased in homosexual men. Little is known about the serologic response to HPV in normal or immunosuppressed men; therefore, HIV-infected and -uninfected homosexual men were screened for HPV-6 and -16 capsid antibodies. HIV-infected men had increased HPV DNA detection but did not significantly differ in the prevalence of serum HPV antibodies. HPV-6 DNA detection and the presence of anal warts were significantly correlated with serum antibody overall and in the HIV-infected subgroup. HPV-16 DNA detection was not significantly correlated with serum antibody overall or in either subgroup; however, HIV-infected men with high-grade anal squamous intraepithelial lesions were significantly more likely to have HPV-16 antibodies. HIV-infected men are able to generate an antibody response to HPV, and a lack of serum HPV antibodies cannot explain the increased HPV-associated disease seen in HIV-infected men.

The relationship of human papillomavirus-related cervical tumors to cigarette smoking, oral contraceptive use, and prior herpes simplex virus type 2 infection

It has now been established that infection with human papillomavirus (HPV) is necessary for the development of most cervical cancers. HPV is not sufficient for the development of cancer. Other exposures or host factors are necessary for cancer to occur. As part of an ongoing, population-based case-control study of invasive cervical cancer, we investigated the role of cigarette smoking, oral contraceptive (OC) use, and herpes simplex virus type 2 (HSV-2) as potential cofactors with HPV in the development of cervical cancer. Residents of three counties in western Washington State who were diagnosed with invasive squamous cell cervical cancer (n = 314) from January 1986 through December 1992 were interviewed about their sexual, reproductive, contraceptive, and cigarette smoking histories. Similar information was obtained from control women identified through random digit dialing (n = 672). The sera from 206 cases and 522 controls were tested for both HPV 16 capsid antibodies and HSV-2 antibodies. PCR was used to test paraffin-embedded tumor tissues for the presence of HPV DNA types 6, 16, 18, 31, 33, 35, and 39. Women with cervical cancer were more likely to be current smokers at diagnosis than population controls [relative risk (RR), 2.5; 95% confidence interval (CI), 1.8-3.4]. The risk associated with smoking was present to a similar extent among women positive and negative for HPV as measured by HPV 16 capsid antibodies and HPV DNA in the tumor tissue (cases). OC use was only important if first use was at an early age, particularly ages < or = 17 years (RR, 2.3; 95% CI, 1.4-3.8). There was only a slight risk for cervical cancer associated with antibodies to HSV-2 (RR, 1.2; 95% CI, 0.9-1.7). However, when we stratified by markers of HPV exposure, we found a significant increase in risk associated with HSV-2 among women negative for HPV 16 antibodies (RR, 2.0; 95% CI, 1.3-3.0), which was strengthened when we confined our analysis to cases whose tumors were HPV DNA negative (RR, 3.6; 95% CI, 1.6-8.0). There was no indication that cigarette smoking, OC use, or HSV-2 infection influence the ability of HPV infection to cause invasive cervical cancer. OC use may only be important in the etiology of invasive squamous cell cervical tumors if the use occurs at a critical time in the development of a woman's reproductive tract, at ages < or = 17 years. The majority of risk associated with HSV-2 was confined to HPV-negative tumors, indicating a possible separate pathway to disease that may account for 5-10% of invasive cervical cancers.

Use of human papillomavirus type 6 capsids to detect antibodies in people with genital warts

Human papillomavirus (HPV) type 6 capsids were produced by recombinant vaccinia viruses and used in a capture ELISA to screen 901 human sera from three studies of genital HPVs. The highest seroprevalence was observed among subjects with recurrent genital warts. In a population-based case-control study of genital warts, 26 (58%) of 45 women with recurrent genital warts were seropositive compared with 19 (19%) of 101 control women with no history of genital warts (odds ratio, 6.5; 95% confidence interval, 3.0, 14.1). Among a cohort of pregnant women, 7 (88%) of 8 with recurrent warts were seropositive compared with 24 (30%) of 79 pregnant women with no such history. A significant association between seropositivity to HPV-6 capsids and the detection of HPV-6/11 DNA from genital specimens by polymerase chain reaction was also observed. Men with genital warts were less likely to be seropositive than were women with genital warts, and a positive association between the number of sex partners and seropositivity was observed among only the female university students.

Immunization of mice with HPV vaccinia virus recombinants generates serum IgG, IgM, and mucosal IgA antibodies

To assess the utility of vaccinia virus recombinants in the development of an immune response against HPV capsid antigens, 5-week-old C57B16 female mice were administered either purified HPV 1 capsids produced by a vaccinia virus recombinant or the recombinant vaccinia virus itself. Animals were boosted at Week 4 with either agent. Mice developed a serum IgG antibody response in all the administration protocols that was directed mainly against native L1 epitopes. Mice injected initially with the vaccinia virus recombinant and boosted with purified capsids had a higher titer antibody response (P = 0.024) with more mice responding to a greater extent. All mice produced a serum IgM response that preceded the IgG response by approximately 2 weeks and lasted 1-3 weeks. The IgM response was directed against native L1 epitopes. Although no serum IgA was detected, IgA could be detected in vaginal secretions of mice that were immunized or boosted with the vaccinia virus vector. These results indicate that an extensive humoral immune response to HPV can be elicited using vaccinia virus recombinants.

Brain abscess following marrow transplantation: experience at the Fred Hutchinson Cancer Research Center, 1984-1992

The etiology of brain abscess in patients undergoing marrow transplantation at the Fred Hutchinson Cancer Research Center in Seattle was assessed in a retrospective review. Fifty-eight patients with histology- or culture-proven brain abscess diagnosed between January 1984 and March 1992 were identified. A fungus was isolated in 92% of cases. Aspergillus species were the most prevalent fungi (58% of cases), and Candida species were second in frequency (33%); sporadic cases were caused by Rhizopus, Absidia, Scopulariopsis, and Pseudallescheria species. Bacteria were involved in fewer than 10% of cases. There was no appreciable variation from year to year in the incidence of brain abscess over this period. Aspergillus brain abscess was associated with concomitant pulmonary disease (87% of cases), whereas candida brain abscess often occurred in association with fungemia (63% of cases) or neutropenia (63%). Mortality was high (97%); the risk of death was unrelated to etiology or therapeutic regimen. Since the etiology of brain abscess in patients undergoing marrow transplantation is primarily fungal, the development of better antifungal therapeutic and/or prophylactic modalities is warranted.

Three-dimensional structure of vaccinia virus-produced human papillomavirus type 1 capsids

The capsid proteins of papillomavirus self-assemble to form empty capsids or virus-like particles that appear quite similar to naturally occurring virions by conventional electron microscopy. To characterize such virus-like particles more fully, cryoelectron microscopy and image analysis techniques were used to generate three-dimensional reconstructions of capsids produced by vaccinia virus recombinants (V capsids) that expressed human papillomavirus type 1 L1 protein only or both L1 and L2 proteins. All V capsids had 72 pentameric capsomers arranged on a T = 7 icosahedral lattice. Each particle (approximately 60 nm in diameter) consisted of an approximately 2-nm-thick shell of protein with a radius of 22 nm with capsomers that extend approximately 6 nm from the shell. At a resolution of 3.5 nm, both V capsid structures appear identical to the capsid structure of native human papillomavirus type 1 (T. S. Baker, W. W. Newcomb, N. H. Olson, L. M. Cowsert, C. Olson, and J. C. Brown, Biophys. J. 60:1445-1456, 1991), thus implying that expressed and native capsids are structurally equivalent.

Campylobacter jejuni bacteremia and Guillain-Barré syndrome in a patient with GVHD after allogeneic BMT

Guillain-Barré syndrome is a rare neurologic complication after allogeneic BMT. In the non-transplant setting, Guillain-Barré syndrome has typically been associated with antecedent acute infections and numerous reports have suggested an association between Campylobacter jejuni infection and the subsequent development of Guillain-Barré syndrome. Thus far, however, reports of C. jejuni-associated Guillain-Barré syndrome have been limited to gastrointestinal C. jejuni infections and none has been reported in BMT transplant patients. We report a case of C. jejuni bacteremia associated with Guillain-Barré syndrome that developed in a patient with chronic GVHD approximately 1 year after allogeneic BMT. The patient was treated with intravenous immunoglobulin and intravenous ciprofloxacin and had partial recovery. Our report illustrates that Guillain-Barré syndrome can occur in association with C. jejuni bacteremia and is a rare cause of polyneuropathy after BMT.

Self-assembly of human papillomavirus type 1 capsids by expression of the L1 protein alone or by coexpression of the L1 and L2 capsid proteins

Vaccinia virus vectors were used to express the major (L1) and minor (L2) capsid proteins of human papillomavirus type 1 (HPV-1) with the vaccinia virus early (p7.5K) or late (pSynth, p11K) promoters. All constructs expressed the appropriate-sized HPV proteins, and both L1 and L2, singly or in combination, localized to the nucleus. Capsids were purified by cesium chloride density gradient centrifugation from nuclei of cells infected with a vaccinia virus-L1 (vac-L1) recombinant or a vac-L1-L2 recombinant but not from vac-L2-infected cells. Electron microscopy showed that the particles were 55 nm in diameter and had icosahedral symmetry. Immunogold-labeled antibodies confirmed the presence of the L1 and L2 proteins in the HPV-1 capsids. Capsids containing L1 alone were fewer and more variable in size and shape than capsids containing the L1 and L2 proteins. The L1-plus-L2 capsids were indistinguishable in appearance from HPV-1 virions obtained from plantar warts. The ability to produce HPV capsids in vitro will be useful in many studies of HPV pathogenicity.

Hyperthyroidism induced by iodinated glycerol

We report a case of iodide-induced thyrotoxicosis after the use of iodinated glycerol (Organidin) for the symptomatic treatment of chronic obstructive pulmonary disease. In patients with severe chronic obstructive pulmonary disease, symptoms of hyperthyroidism may be overlooked. Hyperthyroidism may be induced by any iodinated expectorant, especially in patients with preexisting thyroid disease.

Bleomycin-treated DNA is specifically cleaved only by endonuclease IV in E. coli

We have isolated an endonuclease from E. coli active on bleomycin-treated DNA. Purification on DEAE-cellulose separated this activity in strains lacking endonuclease I, endonuclease III or exonuclease III. After DEAE chromatography, the enzyme was active in the absence of divalent cations and was not inhibited by tRNA or harmane. In addition, this enzyme was stable at 45 degrees C for 20 min. These properties are consistent with this activity being endonuclease IV. This was supported by our finding no activity in a strain lacking endonuclease IV.

Multiple pathways for repair of hydrogen peroxide-induced DNA damage in Escherichia coli

The repair response of Escherichia coli to hydrogen peroxide has been examined in mutants which show increased sensitivity to this agent. Four mutants were found to show increased in vivo sensitivity to hydrogen peroxide compared with wild type. These mutants, in order of increasing sensitivity, were recA, polC, xthA, and polA. The polA mutants were the most sensitive, implying that DNA polymerase I is required for any repair of hydrogen peroxide damage. Measurement of repair synthesis after hydrogen peroxide treatment demonstrated normal levels for recA mutants, a small amount for xthA mutants, and none for polA mutants. This is consistent with exonuclease III being required for part of the repair synthesis seen, while DNA polymerase I is strictly required for all repair synthesis. Sedimentation analysis of cellular DNA after hydrogen peroxide treatment showed that reformation was absent in xthA, polA, and polC(Ts) strains but normal in a recA cell line. By use of a lambda phage carrying a recA-lacZ fusion, we found hydrogen peroxide does not induce the recA promoter. Our findings indicate two pathways of repair for hydrogen peroxide-induced DNA damage. One of these pathways would utilize exonuclease III, DNA polymerase III, and DNA polymerase I, while the other would be DNA polymerase I dependent. The RecA protein seems to have little or no direct function in either repair pathway.

DNA polymerase III requirement for repair of DNA damage caused by methyl methanesulfonate and hydrogen peroxide

The pcbA1 mutation allows DNA replication dependent on DNA polymerase I at the restrictive temperature in polC(Ts) strains. Cells which carry pcbA1, a functional DNA polymerase I, and a temperature-sensitive DNA polymerase III gene were used to study the role of DNA polymerase III in DNA repair. At the restrictive temperature for DNA polymerase III, these strains were more sensitive to the alkylating agent methyl methanesulfonate (MMS) and hydrogen peroxide than normal cells. The same strains showed no increase in sensitivity to bleomycin, UV light, or psoralen at the restrictive temperature. The sensitivity of these strains to MMS and hydrogen peroxide was not due to the pcbAl allele, and normal sensitivity was restored by the introduction of a chromosomal or cloned DNA polymerase III gene, verifying that the sensitivity was due to loss of DNA polymerase III alpha-subunit activity. A functional DNA polymerase III is required for the reformation of high-molecular-weight DNA after treatment of cells with MMS or hydrogen peroxide, as demonstrated by alkaline sucrose sedimentation results. Thus, it appears that a functional DNA polymerase III is required for the optimal repair of DNA damage by MMS or hydrogen peroxide.

DNA polymerase III of Escherichia coli is required for UV and ethyl methanesulfonate mutagenesis

Strains of Escherichia coli possessing the pcbA1 mutation, a functional DNA polymerase I, and a temperature-sensitive mutation in DNA polymerase III can survive at the restrictive temperature (43 degrees C) for DNA polymerase III. The mutation rate of the bacterial genome of such strains after exposure to either UV light or ethyl methanesulfonate was measured by its rifampicin resistance or amino acid requirements. In addition, Weigle mutagenesis of preirradiated lambda phage was also measured. In all cases, no increase in mutagenesis was noted at the restrictive temperature for DNA polymerase III. Introduction of a cloned DNA polymerase III gene returned the mutation rate of the bacterial genome as well as the Weigle mutagenesis to normal at 43 degrees C. Using a recA-lacZ fusion, the SOS response after UV irradiation was measured and found to be normal at the restrictive and permissive temperature for DNA polymerase III, as was induction of lambda prophage. Recombination was also normal at either temperature. Our studies demonstrate that a functional DNA polymerase III is strictly required for mutagenesis at a step other than SOS induction.

Repair response of Escherichia coli to hydrogen peroxide DNA damage

The repair response of Escherichia coli to hydrogen peroxide-induced DNA damage was investigated in intact and toluene-treated cells. Cellular DNA was cleaved after treatment by hydrogen peroxide as analyzed by alkaline sucrose sedimentation. The incision step did not require ATP or magnesium and was not inhibited by N-ethylmaleimide (NEM). An ATP-independent, magnesium-dependent incorporation of nucleotides was seen after the exposure of cells to hydrogen peroxide. This DNA repair synthesis was not inhibited by the addition of NEM or dithiothreitol. In dnaB(Ts) strain CRT266, which is thermolabile for DNA replication, normal levels of DNA synthesis were found at the restrictive temperature (43 degrees C), showing that DNA replication was not necessary for this DNA synthesis. Density gradient analysis also indicated that hydrogen peroxide inhibited DNA replication and stimulated repair synthesis. The subsequent reformation step required magnesium, did not require ATP, and was not inhibited by NEM, in agreement with the synthesis requirements. This suggests that DNA polymerase I was involved in the repair step. Furthermore, a strain defective in DNA polymerase I was unable to reform its DNA after peroxide treatment. Chemical cleavage of the DNA was shown by incision of supercoiled DNA with hydrogen peroxide in the presence of a low concentration of ferric chloride. These findings suggest that hydrogen peroxide directly incises DNA, causing damage which is repaired by an incision repair pathway that requires DNA polymerase I.