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Biomedical subjects

S Prakash

Publications and source records attributed to S Prakash.

At least 163 records · Page 9Linked to original sources
PubMed1995

Comparative activity of three repellents against bedbugs Cimex hemipterus (Fabr.).

Comparative activity of three repellents viz., diethyl-m-toluamide (DEET), diethyl phenyl-acetamide (DEPA) and dimethylphthalate (DMP) against bedbugs Cimex hemipterus (Fabr) was studied by applying repellent solution on the shaven skin of rabbits. DEET (Tech. grade) 20mgai/cm2 exhibited 93 and 83 per cent repellency after 2 and 8 h respectively, while DEPA (Tech. grade) at this concentration exhibited 90 and 71 per cent repellency. DEET and DEPA at 75 per cent concentration (15mgai/cm2) showed 85 and 78 per cent repellency up to 2 h and 52 and 42 per cent repellency 6 h after treatment respectively. The repellent activity was also found to be concentration and time of treatment dependent in respect of DEET and DEPA. DMP (Tech. grade) did not show any appreciable repellent activity at any concentration tested. Further, the blood intake by C. hemipterus following treatment with various concentrations of repellents was found to decrease with increase in the concentration of repellents.

Animals↗
PubMed1995

A role for nongovernmental organizations in monitoring the iodine content of salt in northern India.

The feasibility of using nongovernmental organizations (NGOs) to monitor the iodine content of salt was studied in Uttar Pradesh, northern India, where iodine-deficiency disorders (IDDs) are endemic. Three NGOs already involved in health and development activities in the Gorakhpur, Varanasi, and Dehradun regions collected salt samples monthly from households and shops in selected villages over a 6-month period. A total of 4001 samples were analysed at regional laboratories by trained personnel using a standard protocol; 10% of the samples were sent to a central laboratory for external quality control. The iodine content lay in the range 0-95 mg/kg of salt; it was particularly low in the Gorakhpur and Varanasi regions, where over 80% of samples contained less than the minimum recommended level of 15 mg/kg; 37% of samples were in this category in the Dehradun region. Regular monitoring of the iodine content of salt at the consumer level is essential for the elimination of IDDs, and there is a need to improve awareness of this at all levels. NGOs can play a valuable role in both of these respects.

Humans↗
PubMed1994

A conserved 5' to 3' exonuclease activity in the yeast and human nucleotide excision repair proteins RAD2 and XPG.

Saccharomyces cerevisiae RAD2 protein and its human homolog xeroderma pigmentosum group G (XPG) protein function in the incision step of nucleotide excision repair of DNA damaged by ultraviolet light. Both RAD2 and XPG proteins have been shown previously to possess an endonuclease activity. Using DNA substrates labeled at either the 5' end or 3' end, we now demonstrate that RAD2 protein also digests both single-stranded and double-stranded DNAs exonucleolytically with a 5' to 3' directionality. A 5' to 3' exonuclease activity is also present in the XPG protein, indicating evolutionary conservation of this activity. The possible role of RAD2 and XPG 5' to 3' exonuclease activity in nucleotide excision repair is discussed.

Base Sequence↗
PubMed1994

Yeast DNA repair protein RAD5 that promotes instability of simple repetitive sequences is a DNA-dependent ATPase.

The RAD5 gene of Saccharomyces cerevisiae functions in postreplication repair of ultraviolet damaged DNA, and interestingly, it also has a role in increasing the instability of simple repetitive sequences in the genome. In contrast to DNA mismatch repair genes which function in maintaining constant length of repeat sequences, RAD5 promotes alterations in the length of repeat sequences. In this work, we purify the RAD5 protein to near homogeneity from yeast cells and show that it is a single-stranded DNA-dependent ATPase. The possible roles of RAD5 ATPase in postreplication gap filling and in increasing the incidence of length alterations of repeat sequences are discussed.

Adenosine Triphosphatases↗
PubMed1994

Holliday junction cleavage by yeast Rad1 protein.

In Saccharomyces cerevisiae, of the many genes required for excision repair of ultraviolet-damaged DNA, only RAD1 and RAD10 also function in genetic recombination. Complex formation between the RAD1 and RAD10 gene products activates an endonucleolytic function that nicks single-stranded DNA and negatively supercoiled double-stranded DNA. To characterize the recombination role of the proteins Rad1 and Rad10, we have investigated their interaction with the Holliday junction, a four-stranded structure that results from single-stranded crossover between two duplex DNA molecules and whose resolution is obligatory for the generation of mature recombinants. We show that Rad1 binds specifically to a Holliday junction and, in the presence of magnesium, catalyses the endonucleolytic cleavage of the junction. Junction cleavage by Rad1 proceeds sufficiently without Rad10, thus identifying Rad1 as the catalytic subunit of Rad1/Rad10 endonuclease.

Base Sequence↗
PubMed1994

Human xeroderma pigmentosum group G gene encodes a DNA endonuclease.

Because of defective nucleotide excision repair of ultraviolet damaged DNA, xeroderma pigmentosum (XP) patients suffer from a high incidence of skin cancers. Cell fusion studies have identified seven XP complementation groups, A to G. Previous studies have implicated the products of these seven XP genes in the recognition of ultraviolet-induced DNA damage and in incision of the damage-containing DNA strand. Here, we express the XPG-encoded protein in Sf9 insect cells and purify it to homogeneity. We demonstrate that XPG is a single-strand specific DNA endonuclease, thus identifying the catalytic role of the protein in nucleotide excision repair. We suggest that XPG nuclease acts on the single-stranded region created as a result of the combined action of the XPB helicase and XPD helicase at the DNA damage site.

Animals↗
PubMed1994

RAD25 is a DNA helicase required for DNA repair and RNA polymerase II transcription.

The RAD25 gene of Saccharomyces cerevisiae functions in nucleotide excision repair of ultraviolet-damaged DNA and is also required for cell viability. The RAD25 protein shows remarkable homology to the protein encoded by the human nucleotide-excision-repair gene XPB (ERCC3), mutations in which cause the cancer-prone disease xeroderma pigmentosum and also Cockayne's syndrome. Here we purify RAD25 protein from S. cerevisiae and show that it contains single-stranded DNA-dependent ATPase and DNA helicase activities. Extract from the conditional lethal mutant rad25-ts24 exhibits a thermolabile transcriptional defect which can be corrected by the addition of RAD25 protein, indicating a direct and essential role of RAD25 in RNA polymerase II transcription. The protein encoded by the rad25799am allele is defective in DNA repair but is proficient in RNA polymerase II transcription, indicating that RAD25 DNA-repair activity is separable from its transcription function. The rad25 Arg-392 encoded product, which contains a mutation in the ATP-binding motif, is defective in RNA polymerase II transcription, suggesting that the RAD25-encoded DNA helicase functions in DNA duplex opening during transcription initiation.

Adenosine Triphosphatases↗
PubMed1994

Specific complex formation between yeast RAD6 and RAD18 proteins: a potential mechanism for targeting RAD6 ubiquitin-conjugating activity to DNA damage sites.

The RAD6 gene of Saccharomyces cerevisiae encodes a ubiquitin-conjugating enzyme that is required for postreplication repair of UV-damaged DNA, DNA damage induced mutagenesis, sporulation, and amino-end rule protein degradation. RAD6 interacts physically with the UBR1 gene product in carrying out the multiubiquitination of amino-end rule proteolytic substrates. In mediating postreplication repair, it has remained unclear whether RAD6 acts in a pleiotropic manner distal from the site of DNA damage or is targeted to the damage site via interaction with another repair component. Here, we show that RAD6 forms a specific complex with the product of the DNA repair gene RAD18. The biological significance of this interaction is attested by the observation that overproduction of the rad6 Ala-88 mutant protein, which lacks ubiquitin-conjugating activity but retains the ability to interact with RAD18 protein, confers a high level of UV sensitivity on wild-type RAD+ cells that can be corrected by the concomitant overexpression of RAD18. We demonstrate that whereas RAD6 has no affinity for DNA, RAD18 binds single-stranded DNA. Thus, association of RAD6 with RAD18 could provide a means for targeting RAD6 to damage-containing DNA regions, where the RAD6 ubiquitin-conjugating function could modulate the activity of a stalled DNA replication machinery. We also show that RAD6 forms separate complexes with RAD18 and with UBR1, and the extremely conserved amino terminus of RAD6 that is required for complex formation with UBR1 is dispensable for complex formation with RAD18.

Antibodies, Fungal↗
PubMed1994

The role of reactive oxygen species in the degradation of lindane and DDT.

We have studied the photodegradation reactions of lindane and DDT under sunlight (72 hr) or a solar simulator (2 hr) either directly or in presence of selected photodynamic sensitizers. Direct photolysis did not cause noticeable degradation of the pesticides (below 1% in both the cases). However, addition of benzophenone or rose bengal to the irradiation solution of lindane resulted in 88% and 47% degradation, respectively, under sunlight. Similar experiments carried out with DDT resulted in 89%, 50% and 32% degradation with benzophenone, rose bengal and methylene blue, respectively. All the photosensitizers used for the study have been shown to induce photooxidation reactions by generation of reactive oxygen species. These studies suggest that by employing certain naturally occurring photosensitizers with reactive oxygen generation potential under sunlight, an effective method for safe removal of pesticides and other environmentally persistent agents from the surface of earth can be developed.

Anthracenes↗
PubMed1994

Negative superhelicity promotes ATP-dependent binding of yeast RAD3 protein to ultraviolet-damaged DNA.

The RAD3 gene of Saccharomyces cerevisiae is required for excision repair of UV-damaged DNA and is essential for cell viability. Remarkable homology exists between RAD3 and the human excision repair gene XPD, whose mutational inactivation underlies the cancer-prone disorder in xeroderma pigmentosum group D patients. Our previous work demonstrated that RAD3-encoded protein contains a DNA helicase activity. Here, we show that RAD3 binds preferentially to UV-damaged DNA over nondamaged DNA. Removal of pyrimidine dimers from damaged DNA by enzymatic photoreactivation does not affect binding, suggesting an affinity of RAD3 for pyrimidine (6-4) pyrimidone photoproducts. Damage-specific binding by RAD3 is strongly dependent on ATP and on the degree of negative superhelicity in DNA. The requirement of superhelicity in damage binding may target RAD3 to regions of DNA undergoing transcription, resulting in the preferential repair of these regions. The rad3 Arg-48 mutant protein, which lacks the DNA helicase activity, also binds UV-damaged DNA preferentially, indicating that DNA helicase and damage binding are two distinct and separable functional entities in RAD3.

Adenosine Triphosphatases↗
PubMed1994

DNA repair gene RAD3 of S. cerevisiae is essential for transcription by RNA polymerase II.

The RAD3 gene of Saccharomyces cerevisiae is required for excision repair of ultraviolet-damaged DNA and is essential for cell viability. The RAD3-encoded protein shares a high degree of homology with the human ERCC2(XPD) gene product. Mutations in XPD, besides causing the cancer-prone syndrome xeroderma pigmentosum, can also result in Cockayne's syndrome and trichothiodystrophy. To investigate the role of RAD3 in viability, we examined here the effect of a recessive, temperature-sensitive (ts) conditional lethal mutation of the gene on transcription by RNA polymerase II. Upon transfer to the restrictive temperature, the rad3-ts mutant rapidly ceases growth and poly(A)+ RNA synthesis is inhibited drastically. Messenger RNA levels of all the genes examined, HIS3, TRP3, STE2, MET19, RAD23, CDC7, CDC9 and ACT1, decline rapidly upon loss of RAD3 activity. The synthesis of heat-shock-inducible HSP26 mRNA and galactose-inducible GAL7 and GAL10 mRNAs is also drastically inhibited in the rad3-ts mutant at the restrictive temperature. The RNA polymerase II transcriptional activity in extract from the rad3-ts14 strain is thermolabile, and this in vitro transcriptional defect can be fully corrected by the addition of homogeneous RAD3 protein. These findings indicate that RAD3 protein has a direct and essential role in RNA polymerase II transcription.

Adenosine Triphosphatases↗
PubMed1994

Mosquito repellency & toxicity of isomeric N, N-diethyltolylacetamides.

Three isomers of N, N-diethyltolylacetamides were synthesized and evaluated against Aedes aegypti and Culex quinquefasciatus for repellency and with mice for LD50, as an indicator of mammalian toxicity. Of these, N, N-diethyl-p-tolylacetamide (DEPTA) showed comparatively better repellency against C. quinquefasciatus. All the compounds showed higher repellency against C. quinquefasciatus than Ae. aegypti. In addition, N, N-diethyl-m-tolylacetamide (DEMTA) was found to be least toxic to mice.

Acetamides↗
PubMed1994

A cross-sectional study of subcutaneous fat in well-off north west Indian children.

Attained means and standard deviations of the skinfold thicknesses at triceps, biceps, subscapular and suprailiac sites are presented for 6-16 yr old 589 boys and 566 girls belonging to well-off families residing in Chandigarh, north west India. Girls had larger means throughout the growing period. Limb skinfolds in boys showed a pre-adolescent fatwave followed by a marked decrease in the means. Compared to the British standards, well-off north west Indians had larger triceps and subscapular skinfold thicknesses being closer/above the 75th centile. This agreed well with the observations of earlier workers. Among the possible influencing factors for the fatness of these children, lack of physical activity appeared to be a major one.

Adolescent↗