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Biomedical subjects

N J Robinson

Publications and source records attributed to N J Robinson.

At least 19 recordsLinked to original sources
PubMed2006

Sexual behaviour and condom use among individuals with a history of symptomatic genital herpes.

OBJECTIVES: This study describes the differences in sexual behaviour in individuals with genital herpes (GH) during "symptomatic" and "asymptomatic" periods of the disease. METHODS: A cross sectional questionnaire was undertaken by 1193 individuals attending clinics between 1998 and 2001. All participants in this analysis were in heterosexual, monogamous partnerships, self identified with a history of symptomatic GH and with confirmed HSV-2 infection. RESULTS: Sexual activity reported during asymptomatic v symptomatic periods of GH was 98% v 40% (p<0.001), 76% v 29% (p<0.001), and 25% v 11% (p<0.001) for vaginal, oral, and anal intercourse, respectively, while "always" condom use during asymptomatic and symptomatic periods was 20% v 35% (p<0.001), 2% v 7% (p<0.001), and 10% v 15% (p = 0.131), respectively. The proportion of individuals who either abstained from vaginal intercourse or "always" used condoms was 21% v 74% (p<0.001), for asymptomatic v symptomatic periods. Multivariable analyses indicated that factors associated with engaging in intercourse during symptomatic periods of GH included current intrauterine device use (adjusted odds ratio (aOR) = 2.96, 95% confidence interval (CI) = 1.46 to 6.02); living in Latin America (aOR = 2.16, CI = 1.19 to 3.91) or Europe (aOR = 1.67, CI = 1.21 to 2.28), compared with North America; previous sexually transmitted disease (aOR = 1.42, CI = 1.08 to 1.89); a higher number of sexual acts per month (aOR = 1.09, CI = 1.06 to 1.11); and a higher number of GH recurrences per year (aOR = 1.08, CI = 1.03 to 1.12). CONCLUSIONS: These data indicate that the majority of people with GH either abstained from intercourse or "always" used condoms during symptomatic periods of GH. However, condom use was relatively low during asymptomatic periods in comparison with symptomatic periods. These results highlight that further education on GH prevention is warranted, particularly for symptomatic periods.

Adult↗
PubMed2004

Adolescent sexuality and the HIV epidemic in Yaoundé, Cameroon.

Adolescents are the focus of many interventions that aim to prevent HIV transmission. In order for these interventions to be effective, it is essential to understand adolescents' sexual behaviour. Using data collected in Yaoundé, Cameroon, in 1997, the study analysed risk exposure and HIV prevalence among 426 men and 510 women aged 15-24. Although risky behaviours seem to be more prevalent among young men, their HIV prevalence remains under 1%. In contrast, HIV prevalence is high among young women (7.5%), even those who report having had few sexual partners. Mixing patterns among sexual partners, and especially the age difference between men and women, do not seem to be sufficient to explain the large male-female discrepancy in HIV prevalence that is evident in these data. The results are therefore probably due to a greater susceptibility to infection of young women than men. This study highlights the necessity of reinforcing prevention campaigns among youth and fighting the obstacles that continue to impede the use of condoms in this population.

Adolescent↗
PubMed2004

Performance of focus ELISA tests for herpes simplex virus type 1 (HSV-1) and HSV-2 antibodies among women in ten diverse geographical locations.

To determine the sensitivity and specificity of Focus HerpeSelect ELISAs, sera or plasma samples from women aged 18-55 years were collected in ten cities from eight countries and tested by HerpeSelect HSV-1 ELISA (Focus-HSV-1) and by HerpeSelect HSV-2 ELISA (Focus-HSV-2). Sera with Focus-HSV-2-positive results were retested; 94% of the 3617 samples retested were positive. A subset of sera from each site was then selected, based on the HSV-2 results, and tested by Western blot (WB). The sensitivity and specificity were determined with samples from ten sites (n = 967) for Focus-HSV-1 and from seven sites (n = 675) for Focus-HSV-2. Focus-HSV-1 and WB results were concordant (both negative or both positive) for 97% of samples, with 99% sensitivity and 77% specificity. Specimens from Songkla, Thailand had 84% concordance with WB results for HSV-1, while three other sites had 100% concordance. Concordance of Focus-HSV-2 and WB was 92%, with 97% sensitivity and 89% specificity. Ibadan, Nigeria had 78% concordance. Focus-HSV-2 sensitivity and specificity in sites other than Ibadan were 97% and 93%, respectively. Raising the positive cut-off index value for HSV-2 from 1.1 to 3.5 yielded a sensitivity of 90% and a specificity of 96%. A sensitivity of 90% and a specificity of 98% were achieved for sites other than Nigeria with the higher cut-off. In summary, the sensitivity and specificity of the Focus-HSV-1 and Focus-HSV-2 tests varied by site. Performance data generated in one area may not be applicable to other populations.

Adolescent↗
PubMed2003

Herpes simplex virus type 2 and heterosexual spread of human immunodeficiency virus infection in developing countries: hypotheses and research priorities.

Herpes simplex virus type 2 (HSV-2) infection is almost always sexually transmitted, and causes genital ulceration. Significant progress in our understanding of HSV infection has occurred over the last decade, in part related to the development of accurate and sensitive laboratory tests to study HSV-2. The application of PCR and type-specific serology to individual cases and in population-based studies has enabled the identification of a potentially important role for HSV-2 infection as a cofactor in the sexual transmission of HIV. This is a particular issue in developing countries. This review describes the epidemiology of HSV-2 infection in the HIV era, the hypotheses regarding HSV-HIV interactions, and research priorities for the developing world.

Developing Countries↗
PubMed2003

Seroepidemiological study of herpes simplex virus types 1 and 2 in Brazil, Estonia, India, Morocco, and Sri Lanka.

BACKGROUND: The association between herpes simplex virus type 2 (HSV-2) and human immunodeficiency virus (HIV) and the development of HSV vaccines have increased interest in the study of HSV epidemiology. OBJECTIVES: To estimate the age and sex specific seroprevalence of HSV-1 and HSV-2 infections in selected populations in Brazil, Estonia, India, Morocco, and Sri Lanka. METHODS: Serum samples were collected from various populations including children, antenatal clinic attenders, blood donors, hospital inpatients, and HIV sentinel surveillance groups. STD clinic attenders were enrolled in Sri Lanka, male military personnel in Morocco. Sera were tested using a common algorithm by type specific HSV-1 and HSV-2 antibody assay. RESULTS: 13,986 samples were tested, 45.0% from adult females, 32.7% from adult males, and 22.3% from children. The prevalence of HSV-1 varied by site ranging from 78.5%-93.6% in adult males and from 75.5%-97.8% in adult females. In all countries HSV-1 seroprevalence increased significantly with age (p<0.001) in both men and women. The prevalence of HSV-2 infection varied between sites. Brazil had the highest age specific rates of infection for both men and women, followed by Sri Lanka for men and Estonia for women, the lowest rates being found in Estonia for men and India for women. In all countries, HSV-2 seroprevalence increased significantly with age (p<0.01) and adult females had higher rates of infection than adult males by age of infection. CONCLUSIONS: HSV-1 and HSV-2 seroprevalence was consistently higher in women than men, particularly for HSV-2. Population based data on HSV-1 and HSV-2 will be useful for designing potential HSV-2 vaccination strategies and for focusing prevention efforts for HSV-1 and HSV-2 infection.

Adolescent↗
PubMed2001

A metallothionein containing a zinc finger within a four-metal cluster protects a bacterium from zinc toxicity.

Zinc is essential for many cellular processes, including DNA synthesis, transcription, and translation, but excess can be toxic. A zinc-induced gene, smtA, is required for normal zinc-tolerance in the cyanobacterium Synechococcus PCC 7942. Here we report that the protein SmtA contains a cleft lined with Cys-sulfur and His-imidazole ligands that binds four zinc ions in a Zn(4)Cys(9)His(2) cluster. The thiolate sulfurs of five Cys ligands provide bridges between the two ZnCys(4) and two ZnCys(3)His sites, giving two fused six-membered rings with distorted boat conformations. The inorganic core strongly resembles the Zn(4)Cys(11) cluster of mammalian metallothionein, despite different amino acid sequences, a different linear order of the ligands, and presence of histidine ligands. Also, SmtA contains elements of secondary structure not found in metallothioneins. One of the two Cys(4)-coordinated zinc ions in SmtA readily exchanges with exogenous metal ((111)Cd), whereas the other is inert. The thiolate sulfur ligands bound to zinc in this site are buried within the protein. Regions of beta-strand and alpha-helix surround the inert site to form a zinc finger resembling the zinc fingers in GATA and LIM-domain proteins. Eukaryotic zinc fingers interact specifically with other proteins or DNA and an analogous interaction can therefore be anticipated for prokaryotic zinc fingers. SmtA now provides structural proof for the existence of zinc fingers in prokaryotes, and sequences related to the zinc finger motif can be identified in several bacterial genomes.

Amino Acid Sequence↗
PubMed2001

Two Menkes-type atpases supply copper for photosynthesis in Synechocystis PCC 6803.

Synechocystis PCC 6803 contains four genes encoding polypeptides with sequence features of CPx-type ATPases, two of which are now designated pacS and ctaA. We show that CtaA and PacS (but not the related transporters, ZiaA or CoaT) facilitate switching to the use of copper (in plastocyanin) as an alternative to iron (in cytochrome c(6)) for the carriage of electrons within the thylakoid lumen. Disruption of pacS reduced copper tolerance but enhanced silver tolerance, and pacS-mediated restoration of copper tolerance was used to select transformants. Disruption of ctaA caused no change in copper tolerance but reduced the amount of copper cell(-1). In cultures supplemented with 0.2 microm copper, photooxidation of cytochrome c(6) (PetJ) was depressed in wild-type cells but remained elevated in both Synechocystis PCC 6803(ctaA) and Synechocystis PCC 6803(pacS). Conversely, plastocyanin transcripts (petE) were less abundant in both mutants at this [copper]. Synechocystis PCC 6803(ctaA) and Synechocystis PCC 6803(pacS) showed increased iron dependence with impaired growth in deferoxamine mesylate (iron chelator)-containing media. Double mutants also deficient in cytochrome c(6), Synechocystis PCC 6803(petJ,ctaA) and Synechocystis PCC 6803(petJ,pacS), were viable, but the former had increased copper dependence with severely impaired growth in the presence of bathocuproinedisulfonic acid (copper chelator). Analogous transporters are likely to supply copper to plastocyanin in chloroplasts.

Adenosine Triphosphatases↗
PubMed2001

Microbial metallothioneins.

Bacterial metallothioneins bind, sequester and buffer excess intracellular zinc. At present, the vast majority of the available experimental data relate to cyanobacterial metallothionein, SmtA, from Synechococcus PCC 7942. SmtA is required for normal resistance to zinc and smtA-mediated zinc resistance has been used as a selectable marker. The imidazole groups of histidine residues, in addition to the thiol groups of cysteine residues, co-ordinate zinc in bacterial metallothioneins. The structure of bacterial metallothionein must facilitate some discrimination between 'adventitious' and 'adventageous' zinc-binding sites such that under excess zinc conditions metal is predominantly scavenged from the former. It remains unclear whether or not bacterial metallothionein also acts as a zinc store that supplies zinc-requiring proteins or if under some conditions it deactivates a subset of proteins via zinc removal. Expression of smtA is induced in response to elevated concentrations of zinc via the action of SmtB. SmtB has some sequence similarity to the arsenic responsive repressor ArsR and genes encoding related proteins are present in many bacterial genomes. Metal perception by SmtB differs from ArsR. The latter contains a characteristic Cys-Val-Cys motif associated with a DNA-binding helix-turn-helix (the ArsR motif), while the former contains metal-binding motifs associated with a carboxyl-terminal alpha-helix that forms the interface between SmtB dimers (the SmtB motif). Some SmtB-ArsR family proteins, including the zinc sensor ZiaR from the cyanobacterium Synechocystis PCC 6803, have the metal-sensory motifs of both SmtB and ArsR. The mechanisms of action, and the features that allow discrimination between different metal ions by these sensors, are discussed.

Amino Acid Sequence↗
PubMed2001

Multicentre study on factors determining differences in rate of spread of HIV in sub-Saharan Africa: methods and prevalence of HIV infection.

OBJECTIVE: The objective of this study was to explore whether the differences in rate of spread of HIV in different regions in sub-Saharan Africa could be explained by differences in sexual behaviour and/or factors influencing the probability of HIV transmission during sexual intercourse. METHODS: A cross-sectional, population-based study was conducted in two cities with a high HIV prevalence (Kisumu in Kenya and Ndola in Zambia) and two cities with a relatively low HIV prevalence (Cotonou in Benin and Yaoundé in Cameroon). In each of these cities, approximately 1000 men and 1000 women, aged 15-49 years, were randomly selected from the general population. Consenting men and women were interviewed and were tested for HIV, syphilis, herpes simplex virus type 2 (HSV-2), gonorrhoea, chlamydial infection and trichomoniasis (the latter for women only). In addition, a survey was conducted on a random sample of 300 sex workers in each city. The research instruments, including the questionnaires and the laboratory procedures, were standardized to permit comparison of results. RESULTS: The numbers of men interviewed were 1021 in Cotonou, 973 in Yaoundé, 829 in Kisumu, and 720 in Ndola. The corresponding figures for women were 1095, 1116, 1060 and 1130. In Yaoundé, Kisumu and Ndola, the response rates for men were lower than for women due to failure to make contact with eligible men. The proportion of eligible women who were interviewed was 86% in Yaoundé, and 89% in Kisumu and Ndola. In Yaoundé, 76% of eligible men were interviewed, along with 82% in Kisumu and 75% in Ndola. The prevalence of HIV infection in men was 3.3% in Cotonou, 4.1% in Yaoundé, 19.8% in Kisumu and 23.2% in Ndola. For women, the respective figures were 3.4, 7.8, 30.1 and 31.9%. The prevalence of HIV infection among women aged 15-19 years was 23.0% in Kisumu and 15.4% in Ndola. Among women in Kisumu who had their sexual debut 5 years before the interview, the prevalence of HIV infection was 46%; in Ndola, it was 59%. Among sex workers, the prevalence of HIV infection was 57.5% in Cotonou, 34.4% in Yaoundé, 74.7% in Kisumu and 68.7% in Ndola. CONCLUSIONS: The HIV prevalence rates in the general population confirmed our preliminary assessment of the level of HIV infection in the four cities, which was based on estimates of HIV prevalence from sentinel surveillance among pregnant women. The very high prevalence of HIV infection among young women in Kisumu and Ndola calls for urgent intervention.

Adolescent↗
PubMed2001

Ecological and individual level analysis of risk factors for HIV infection in four urban populations in sub-Saharan Africa with different levels of HIV infection.

OBJECTIVE: To identify factors that could explain differences in rate of spread of HIV between different regions in sub-Saharan Africa. DESIGN: Cross-sectional study. METHODS: The study took place in two cities with a relatively low HIV prevalence (Cotonou, Benin and Yaoundé, Cameroon), and two cities with a high HIV prevalence (Kisumu, Kenya and Ndola, Zambia). In each of these cities, a representative sample was taken of about 1000 men and 1000 women aged 15-49 years. Consenting men and women were interviewed about their socio-demographic background and sexual behaviour; and were tested for HIV, herpes simplex virus type 2 (HSV-2), syphilis, Chlamydia trachomatis and Neisseria gonorrhoea infection, and (women only) Trichomonas vaginalis. Analysis of risk factors for HIV infection was carried out for each city and each sex separately. Adjusted odds ratios (aOR) were obtained by multivariate logistic regression. RESULTS: The prevalence of HIV infection in sexually active men was 3.9% in Cotonou, 4.4% in Yaoundé, 21.1% in Kisumu, and 25.4% in Ndola. For women, the corresponding figures were 4.0, 8.4, 31.6 and 35.1%. High-risk sexual behaviour was not more common in the high HIV prevalence cities than in the low HIV prevalence cities, but HSV-2 infection and lack of circumcision were consistently more prevalent in the high HIV prevalence cities than in the low HIV prevalence cities. In multivariate analysis, the association between HIV infection and sexual behavioural factors was variable across the four cities. Syphilis was associated with HIV infection in Ndola in men [aOR = 2.7, 95% confidence interval (CI) = 1.5-4.91 and in women (aOR = 1.7, 95% CI = 1.1-2.6). HSV-2 infection was strongly associated with HIV infection in all four cities and in both sexes (aOR ranging between 4.4 and 8.0). Circumcision had a strong protective effect against the acquisition of HIV by men in Kisumu (aOR = 0.25, 95% CI = 0.12-0.52). In Ndola, no association was found between circumcision and HIV infection but sample sizes were too small to fully adjust for confounding. CONCLUSION: The strong association between HIV and HSV-2 and male circumcision, and the distribution of the risk factors, led us to conclude that differences in efficiency of HIV transmission as mediated by biological factors outweigh differences in sexual behaviour in explaining the variation in rate of spread of HIV between the four cities.

Adolescent↗
PubMed2001

The epidemiology of gonorrhoea, chlamydial infection and syphilis in four African cities.

OBJECTIVES: To compare the epidemiology of gonorrhoea, chlamydial infection and syphilis in four cities in sub-Saharan Africa; two with a high prevalence of HIV infection (Kisumu, Kenya and Ndola, Zambia), and two with a relatively low HIV prevalence (Cotonou, Benin and Yaoundé, Cameroon). DESIGN: Cross-sectional study, using standardized methods, including a standardized questionnaire and standardized laboratory tests, in four cities in sub-Saharan Africa. METHODS: In each city, a random sample of about 2000 adults aged 15-49 years was taken. Consenting men and women were interviewed about their socio-demographic characteristics and their sexual behaviour, and were tested for HIV, syphilis, herpes simplex virus type 2 (HSV-2), gonorrhoea, chlamydial infection, and (women only) Trichomonas vaginalis infection. Risk factor analyses were carried out for chlamydial infection and syphilis seroreactivity. RESULTS: The prevalence of gonorrhoea ranged between 0% in men in Kisumu and 2.7% in women in Yaoundé. Men and women in Yaoundé had the highest prevalence of chlamydial infection (5.9 and 9.4%, respectively). In the other cities, the prevalence of chlamydial infection ranged between 1.3% in women in Cotonou and 4.5% in women in Kisumu. In Ndola, the prevalence of syphilis seroreactivity was over 10% in both men and women; it was around 6% in Yaoundé, 3-4% in Kisumu, and 1-2% in Cotonou. Chlamydial infection was associated with rate of partner change for both men and women, and with young age for women. At the population level, the prevalence of chlamydial infection correlated well with reported rates of partner change. Positive syphilis serology was associated with rate of partner change and with HSV-2 infection. The latter association could be due to biological interaction between syphilis and HSV-2 or to residual confounding by sexual behaviour. At the population level, there was no correlation between prevalence of syphilis seroreactivity and reported rates of partner change. CONCLUSION: Differences in prevalence of chlamydial infection could be explained by differences in reported sexual behaviour, but the variations in prevalence of syphilis seroreactivity remained unexplained. More research is needed to better understand the epidemiology of sexually transmitted infections in Africa.

Adolescent↗
PubMed2001

The epidemiology of trichomoniasis in women in four African cities.

OBJECTIVES: To describe the epidemiology of Trichomonas vaginalis infection and its association with HIV infection, in women in four African cities with different levels of HIV infection. DESIGN: Cross-sectional study, using standardized methods, including a standardized questionnaire and standardized laboratory tests, in four cities in sub-Saharan Africa: two with a high prevalence of HIV infection (Kisumu, Kenya and Ndola, Zambia), and two with a relatively low prevalence of HIV (Cotonou, Benin and Yaoundé, Cameroon). METHODS: In each city, a random sample of about 2000 adults aged 15-49 years was taken. Consenting men and women were interviewed about their socio-demographic characteristics and their sexual behaviour, and were tested for HIV, syphilis, herpes simplex virus type 2 (HSV-2), gonorrhoea, chlamydial infection, and (women only) T. vaginalis infection. Risk factor analyses were carried out for trichomoniasis for each city separately. Multivariate analysis, however, was only possible for Yaoundé, Kisumu and Ndola. RESULTS: The prevalence of trichomoniasis was significantly higher in the high HIV prevalence cities (29.3% in Kisumu and 34.3% in Ndola) than in Cotonou (3.2%) and Yaoundé (17.6%). Risk of trichomoniasis was increased in women who reported more lifetime sex partners. HIV infection was an independent risk factor for trichomonas infection in Yaoundé [adjusted odds ratio (OR) = 1.8, 95% confidence interval (CI) = 0.9-3.7] and Kisumu (adjusted OR = 1.7, 95% CI = 1.1-2.7), but not in Ndola. A striking finding was the high prevalence (40%) of trichomonas infection in women in Ndola who denied that they had ever had sex. CONCLUSION: Trichomoniasis may have played a role in the spread of HIV in sub-Saharan Africa and may be one of the factors explaining the differences in levels of HIV infection between different regions in Africa. The differences in prevalence of trichomoniasis between the four cities remain unexplained, but we lack data on the epidemiology of trichomoniasis in men. More research is required on the interaction between trichomoniasis and HIV infection, the epidemiology of trichomoniasis in men, and trichomonas infections in women who deny sexual activity.

Adolescent↗
PubMed2001

The epidemiology of HSV-2 infection and its association with HIV infection in four urban African populations.

OBJECTIVES: To estimate age- and sex-specific herpes simplex virus type-2 (HSV-2) prevalence in urban African adult populations and to identify factors associated with infection. DESIGN AND METHODS: Cross-sectional, population-based samples of about 2000 adults interviewed in each of the following cities: Cotonou, Benin; Yaoundé, Cameroon; Kisumu, Kenya and Ndola, Zambia. Consenting study participants were tested for HIV, HSV-2 and other sexually transmitted infections. RESULTS: HSV-2 prevalence was over 50% among women and over 25% among men in Yaoundé, Kisumu and Ndola, with notably high rates of infection among young women in Kisumu and Ndola (39% and 23%, respectively, among women aged 15-19 years). The prevalence in Cotonou was lower (30% in women and 12% in men). Multivariate analysis showed that HSV-2 prevalence was significantly associated with older age, ever being married, and number of lifetime sexual partners, in almost all cities and both sexes. There was also a strong, consistent association with HIV infection. Among women, the adjusted odds ratios for the association between HSV-2 and HIV infections ranged from 4.0 [95% confidence interval (CI) = 2.0-8.0] in Kisumu to 5.5 (95% CI = 1.7-18) in Yaoundé, and those among men ranged from 4.6 (95% CI = 2.7-7.7) in Ndola to 7.9 (95% CI = 4.1-15) in Kisumu. CONCLUSIONS: HSV-2 infection is highly prevalent in these populations, even at young ages, and is strongly associated with HIV at an individual level. At a population level, HSV-2 prevalence was highest in Kisumu and Ndola, the cities with the highest HIV rates, although rates were also high among women in Yaoundé, where there are high rates of partner change but relatively little HIV infection. The high prevalence of both infections among young people underlines the need for education and counselling among adolescents.

Adolescent↗
PubMed2000

Epidemiology in the pharmaceutical industry: a perspective for infectious diseases.

As access to observational data and databases expands so does the need for epidemiologists in industry. As an example, in the U.K. arm of the Department of Epidemiology at GlaxoWellcome Research and Development, the number of PhD-trained epidemiologists increased from zero in 1996 to eight in 1999. Their remit is often broad, including designing and co-ordinating, pharmacoepidemiologic research, studies of risk factors for disease and disease progression and pregnancy registries. Where appropriate, existing data sources, such as research databases, are employed for studies. Otherwise, primary data collection is pursued using standard methodology, for example, cross-sectional, case-control and cohort studies. This paper describes a structure for epidemiologic research in the pharmaceutical industry, the role of the industry epidemiologist and the scope of epidemiological studies. Two examples of observational studies of HSV-2/HIV interactions are given, and implications for research agendas discussed. The pharmaceutical industry is becoming increasingly committed to epidemiological research, and research agendas often involve extensive collaboration with leading external academic and public health groups.

Adolescent↗
PubMed2000

HIV infection in Poland (1985-96).

Reported numbers of HIV infections have provided an indication of the order of magnitude of the size of the HIV epidemic in Poland, and how it has evolved in time. To the end of 1996, most documented infections had been observed among intravenous drug users (IDUs, n=2, 933/3,470) and, to a lesser extent, men who have sex with men (MSM, 289/3,470). Reported infections among non-IDU prostitutes and other non-IDU heterosexuals remained low. In this paper we describe surveillance systems and epidemiologic data in Poland from 1985 to 1996 for AIDS cases, HIV infections and other STDs. We also discuss the contributions of different vulnerable groups. Finally we discuss factors influencing the past spread of HIV infection and the potential for future spread, and propose recommendations for surveillance and research.

Acquired Immunodeficiency Syndrome↗
PubMed1999

Cobalt-dependent transcriptional switching by a dual-effector MerR-like protein regulates a cobalt-exporting variant CPx-type ATPase.

CoaR associates with and confers cobalt-dependent activation of the coaT operator-promoter. A CoaR mutant (Ser-Asn-Ser) in a carboxyl-terminal Cys-His-Cys motif bound the coaT operator-promoter but did not activate expression in response to cobalt, implicating thiolate and/or imidazole ligands at these residues in an allosteric cobalt binding site. Deletion of 1 or 2 nucleotides from between near consensus, but with aberrant (20 base pairs) spacing, -10 and -35 elements enhanced expression from the coaT operator-promoter but abolished activation by cobalt-CoaR. It is inferred that cobalt effects a transition in CoaR that underwinds the coaT operator-promoter to realign promoter elements. In the absence of cobalt, CoaR represses expression (approximately 50%). CoaR is a fusion of ancestral MerR (mercury-responsive transcriptional activator)- and precorrin isomerase (enzyme of vitamin B(12) biosynthesis)-related sequences. Expression from the coaT operator-promoter was enhanced in a partial mutant of cbiE (encoding an enzyme preceding precorrin isomerase in B(12) biosynthesis), revealing that this pathway "inhibits" coaT expression. Disruption of coaT reduced cobalt tolerance and increased cytoplasmic (57)Co accumulation. coaT-mediated restoration of cobalt tolerance has been used as a selectable marker.

Adenosine Triphosphatases↗