In this task, you are given a passage which has a question and the context. You have to generate an answer to the question based on the information present in the context.

Q: Context: The blasticidin S resistance gene (bsr) is a selectable marker used for gene transfer experiments. The bsr gene encodes for blasticidin S (BS) deaminase, which has a specific activity upon BS. Therefore, its expression is supposed to be harmless in cells. The work reported on herein consisted of experiments to verify a possible toxicity of bsr on mammalian cells, which include several cell lines and primary cultures.', 'Murine keratinocyte BALB/MK and human primary keratinocyte cells transduced with the retroviral vector LBmSN, which has an improved expression system of bsr, namely bsrm, died in five days after the transduction. Meanwhile the control vector LBSN, which expresses bsr, did not provoke cell death. The lethal activity of bsrm was observed only in human keratinocytes and BALB/MK cells among the cell types tested here. Death appears to be mediated by a factor, which is secreted by the BALB/MK transduced cells.\Question: Is over expression of the selectable marker blasticidin S deaminase gene toxic to human keratinocytes and murine BALB/MK cells?

A: By our study we demonstrated that the expression of bsrm gene is toxic to human keratinocytes and BALB/MK cells. It is likely over expression of BS deaminase gene is responsible for the death.
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Q: Context: To determine the extent of genetic variation among internationally collected HIV-1 isolates, to analyse phylogenetic relationships and the geographic distribution of different variants.', 'Phylogenetic comparison of 70 HIV-1 isolates collected in 15 countries on four continents.', 'To sequence the complete gag genome of HIV-1 isolates, build multiple sequence alignments and construct phylogenetic trees using distance matrix methods and maximum parsimony algorithms.', 'Phylogenetic tree analysis identified seven distinct genotypes. The seven genotypes were evident by both distance matrix methods and maximum parsimony analysis, and were strongly supported by bootstrap resampling of the data. The intra-genotypic gag distances averaged 7%, whereas the inter-genotypic distances averaged 14%. The geographic distribution of variants was complex. Some genotypes have apparently migrated to several continents and many areas harbor a mixture of genotypes. Related variants may cluster in certain areas, particularly isolates from a single city collected over a short time.\Question: Does phylogenetic analysis of gag genes from 70 international HIV-1 isolates provide evidence for multiple genotypes?

A: The genetic variation among HIV-1 isolates is more extensive than previously appreciated. At least seven distinct HIV-1 genotypes can be identified. Diversification, migration and establishment of local, temporal 'blooms' of particular variants may all occur concomitantly.
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Q: Context: Selenium is an essential mineral for immunological function, performing crucial functions at the cellular level. This micronutrient has been determined to be frequently deficient in HIV infected patients, with correlations between reduced immunological function and greater susceptibility to opportunistic infections. Our aim was to evaluate the influence of time of exposure to antiretroviral therapy (ART) on the biochemical profile of selenium in HIV-infected patients.', 'We performed a cross-sectional study on 50 HIV-positive men with different quantitations of viral load and CD4+ T cells, who were either receiving or not receiving ART. Dual energy X-ray absorptiometry (DXA) to determine body composition, biochemical analysis of selenium and albumin, anthropometric measurements were performed. The subjects were divided into groups according to the use of ART or not: The Control Group (CG) was 10 treatment-naïve volunteers, Group G < 2 was 20 volunteers on ART for less than 2 years, and Group G > 2 was 20 volunteers on ART for >2 years.', 'The body mass index showed that all subjects were of normal weight. The group with a longer time of exposure to ART (G > 2) had undetectable viremia and a higher CD4+ T cell count: 593.1 ± 234.6 mm(3). Selenium values (μg/L) were 55.9 ± 11.9 for CG, 52.1 ± 10.5 for G < 2, and 66.9 ± 20.8 for G > 2, with a significant difference between groups G < 2 and G > 2 (p < 0.05), and only G > 2 showed normal selenium values.\Question: Does a longer time of exposure to antiretroviral therapy improve selenium levels?

A:
Most of the men studied showed selenium deficiency, except for the subjects with a longer exposure to antiretroviral treatment. Thus, an adequate selenium concentration is related to better control of virology and of immunologic function.
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