Biomedical subjects
G Karthikeyan
Publications and source records attributed to G Karthikeyan.
RecA interacts with Klenow and enhances fidelity of DNA synthesis in vitro.
To understand the molecular basis of RecA-mediated DNA-repair, we tested the replicative fidelity of the large fragment of Pol I (Klenow) in RecA-DNA complexes in vitro. Klenow synthesis was error-prone in naked DNA substrates but essentially error-free in RecA coated complexes. Escherichia coli SSB, causes no such improvement in Klenow fidelity. RecA filaments promote better exonucleolytic proofreading by Klenow than on naked DNA substrates at select sites when replication is "stalled" due to a missing dNTP. Addition of RecA to pyrene sulfonylchloride-labeled Klenow resulted in a specific increase in steady-state fluorescence anisotropy and a concomitant decrease in fluorescence lifetime. These observations suggest the possibility of a direct interaction between RecA and Klenow even in the absence of DNA which may mediate the observed improvement in Klenow fidelity.
Non-Watson-Crick base pairs modulate homologous alignments in RecA pairing reactions.
Complementary pairing by RecA was examined in vitro to investigate how homology is deciphered from non-homology. Somewhere in a window of 40-50% sequence complementarity, RecA pairing begins to manifest the specificity of homology. Quantitation reveals a hierarchy among non-Watson-Crick mispairs: RecA reaction treats six out of 12 possible mispairs as good ones and three each of the remaining ones as moderate and bad pairs. The mispairs seem to function as independent pairing units free of sequence context effects. The overall strength of pairing is simply the sum of the constituent units. RecA mediated gradation of mispairs, free of sequence context effects, might offer a general thumb-rule for predicting the pairing strength of any alignment that carries multiple mispairs.
Immunogenic response to hepatitis B vaccine in Indian infants.
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Photooxidant injury to glucose-6-phosphate dehydrogenase-deficient erythrocytes with bilirubin as the sensitizer--an in vitro study.
To evaluate the hypothesis that glucose-6-phosphate dehydrogenase (G6PD)-deficient erythrocytes are more prone to photooxidant injury with bilirubin as the sensitizer, we compared the malonyl dialdehyde (MDA) levels and haematocrit values in 11 G6PD-deficient samples with a bilirubin: albumin molar ratio of 1:2 (10 mg% bilirubin, 2.5 g % albumin) photoexposed at 6 microW cm-2 nm-2 (420-460 nm), with 11 of control samples. Twelve hours after photoexposure the incremental changes in MDA levels (OD units) were higher in G6PD-deficient samples [mean (SE) = 0.230 (0.171) vs 0.075 (0.043), p < 0.01]. Antioxidant drugs may have a protective role while G6PD-deficient neonates undergo phototherapy.
Caffeine and fetal growth.
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Immunization for hepatocellular carcinoma.
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Anomalous origin of the left coronary artery from the pulmonary artery: is reconstruction of a double coronary artery system always necessary?
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Fetal pulse oximetry.
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Tricuspid valve endocarditis in a child with structurally normal heart.
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Giant congenital nevocellular nevus and natal teeth.
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Cutaneous ulcers in typhoid fever.
Cutaneous lesions in typhoid fever are uncommon. We report cutaneous ulcers in two children (aged 10 years and 3 years) with typhoid fever.
Involvement of cytochrome P-450 in conferring chloroquine resistance to the malarial parasite, Plasmodium falciparum.
The higher levels of cytochrome P-450 dependent enzyme activities reported earlier are traced to higher levels of cytochrome P-450 (CYPIIB1/B2 like) messenger RNA in the chloroquine resistant than the sensitive strains. The messenger RNA is also induced by phenobarbitone in the sensitive strain. Pretreatment with phenobarbitone affords partial protection to chloroquine toxicity in the sensitive strain and this is not due to a differential accumulation of the drug.
Typhoid fever and nephrotic syndrome--an unusual association.
We report a case of nephrotic syndrome seen in a 9-year-old boy having a significant temporal relationship with culture proven multidrug resistant Salmonella typhi infection. Such an association is quite unusual and probably has not been reported before.