• T Ramakrishnan

      Articles written in Journal of Biosciences

    • Characterisation of rinderpest virus RNA and the action of actinomycin D on its replication

      K Prakash A Antony T Ramakrishnan

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      RNA extracted from purified rinderpest virus was characterised by sucrose gradient sedimentation and polyacrylamide gel electrophoresis. The predominant virion RNA species had a sedimentation constant of 46S and its estimated molecular weight was 4.8 × 106 daltons. Consistently high amounts of UMP and AMP were detected. The melting-temperature profile of the virion RNA suggested absence of secondary structure.

      The effect of actionomycin D on the replication of rinderpest virus in Vero cells was studied by following the viral RNA synthesis using labelled uridine as well as by infectivity titration. The viral RNA synthesis was not affected until 12 h following infection and was inhibited thereafter between 18 and 48 h to an extent of 25% at 5 and 10 Μg levels of the drug. A 100 to 1000-fold reduction in the infectivity titres was observed in the presence of the drug. These results suggest that actinomycin D inhibits rinderpest viral RNA replication. Sedimentation analysis of viral RNA extracted from drug-treated cultures showed inhibition of the genome RNA of rinder-pest virus.

    • Effect of phytohormones on nuclear RNA synthesis in germinating seeds ofTrigonella foenumgraeceum and its callus

      P K Asha M S Shaila C S Vaidyanathan T Ramakrishnan

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      Treatment ofTrigonella foenumgraeceum (fenugreek) seedlings with naphthalene acetic acid plus gibberellic acid enhanced the RNA synthesising capacity of nuclei isolated from the hypocotyl and cotyledonary regions. This increase was more pronounced in the nuclei from the hypocotyl region than from the cotyledonary region.In vitro addition of these phytohormones did not stimulate RNA synthesis by nuclei. The RNA synthesis by mitochondria was not affected by preincubating the seedlings with the hormones. The nuclei isolated from callus cultures of fenugreek hypocotyl treated with the hormone also showed increased RNA synthesis.

    • RNA polymerase activity in isolated nuclei ofNicotiana sanderae callus: Characteristics and modulation during differentiation

      P K Asha M S Shaila C S Vaidyanathan T Ramakrishnan

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      Isolated nuclei from differentiating cultures ofNicotiana sanderae showed increased levels of RNA polymerase activity as compared to the nuclei from callus cultures. The RNA synthetic activity was dependent on nucleotide triphosphates and Mg2+ and was destroyed by RNase. Maximum activity was obtained in the presence of 50 mM (NH4)2 SO4 and α-amanitin inhibited 40% and 55% of the activity in the nuclei from callus and differentiating tissue respectively. The nuclei from differentiating tissue elicited a 3-fold increase in RNA polymerase I and a 4-fold augmentation in RNA polymerase II activities.

    • Studies on the effects ofin vitro methyiation on aminoacylation of transfer RNA

      B R Vani T Ramakrishnan

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      In vitro methyiation ofEscherichia coli transfer ribonucleic acid by cell free extracts ofMycobacterium smegmatis leads exclusively to the formation of 1-methyl adenine [Vani, B. R., Ramakrishnan, T., Taya, Y., Noguchi, S., Yamaiuzumi, Z. and Nishimura, S. (1978)J. Bact., 137, 1085]. We have studied the effect of this modification on aminoacylationof Escherichia coli tRNA by mycobacterial enzymes. Aminoacylation with total algal protein hydrolysate as well as several individual aminoacids like methionine, valine, tyrosine, aspartic acid and lysine were monitored. In all the cases methyiation had a positive effect on the extent of aminoacylation by mycobacterial enzymes. Decreased aminoacylationin vitro was observed when hypomethylated transfer RNA from ethionine treated cells was used as the substrate for aminoacylation

    • Modified bases in transfer RNA

      Vani Brahmachari T Ramakrishnan

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      Transfer RNA is uniquely enriched with modified bases. A large body of information has accumulated about the occurrence, nature and distribution of modified bases in tRNA. But similar investigations on the enzymes involved in this post-transcriptional modification have been hampered by the instability of the enzymes and lack of suitable substrates. The present review summarises briefly, the occurrence and methods of detection of modified bases, the enzymes involved in their formation and also certain suggestive evidence for the role of modification in cellular metabolism.

    • Evaluation of mutagenicity of the antitubercular naphthylglycine hydrazides insalmonella typhimurium

      B Ramamurthy S B Pai T Ramakrishnan

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      N-(2-naphthyl)glycine hydrazide and N-methyl-N-(2-naphthyl) glycine hydrazide, which inhibitMycobacterium tuberculosis H37 RV and show activity against experimental tuberculosis, were evaluated for their mutagenic potential inSalmonella typhimurium. Both the compounds at concentration ranges from 0.1 Μgplate to 1000 Μg/plate failed to induce mutations at the histidine locus either directly or after treatment with rat liver homogenate fraction-“S-9”. N-(2-naphthyl)glycine hydrazide and its N-methyl derivative elicited toxicity at concentrations of 500 Μg/plate and 1000 Μg/plate. However, in the presence of the liver homogenate system, reduction in toxicity was noticed probably due to detoxification and/ or conjugation of the compounds. Under the assay conditions employed, standard mutagens like 4-nitroquinoline-N-oxide, 9-aminoacridine and benzo(a)pyrene were positive. The non-mutagenic nature of N-(2-naphthyl)glycine hydrazide and N-methyl-N-(2-naphthyl)glycine hydrazide should enhance their potential for inclusion in treatment protocols for management of tuberculosis

    • Antigenic relationship between reactivity to hepatitis B e antigen and 19 kDa protein ofMycobacterium tuberculosis among the Tibetan settlers in Karnataka

      Madhuri Apte N Shamala T Ramakrishnan

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      McGlynn and her co-workers have reported that among the Vietnamese refugees in Philadelphia and among Alaskan natives who are hepatitis B carriers, there is a statistically significant association between anegative tuberculin test and the presence of hepatitis B e antigen. A repetition of this work among the population of Bangalore did not yield any significant results because of the very low incidence of hepatitis found among this population. However, on the basis of available data that hepatitis B infection is more prevalent among the Mongolian population than among people of other populations, the work was repeated among Tibetans who had settled down in Karnataka. This set of experiments showed that, contrary to the report of McGlynnet al, there is a statistically significant association between apositive tuberculin test and the presence of hepatitis B e antigen and that those individuals who showed the presence of hepatitis B e antigen exhibited less severe form of the disease than those who were negative to this antigen. These findings suggested that immunity to tuberculosis and hepatitis B infections may have a common underlying principle. Data bank search revealed a stretch of amino acid sequences which is common to hepatitis B e antigen and 19 kDa antigen ofMycobacterium tuberculosis. The significance of these results is discussed.

    • The control of tuberculosis: a continuous game of snakes and ladders

      T Ramakrishnan P Chandrasekhar

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