• M Chakravorty

      Articles written in Journal of Biosciences

    • Effect of supplementation with exogenous fatty acid on the biological properties of a fatty acid requiring auxotroph ofSalmonella typhimurium

      J K Deb S K Biswas P Chakrabati M Chakravorty

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      The effects of changes in fatty acid composition of the cell membrane on different biological functions ofSalmonella typhimurium have been studied with the help of a temperature sensitive fatty acid auxotroph which cannot synthesise unsaturated fatty acids at high temperature. On being shifted to nonpermissive temperature the cells continue growing for another one and half to two generations. The rates of protein and DNA syntheses run parallel to the growth rate but the rate of RNA synthesis is reduced. Further, there is a gradual reduction in the rate of transport of exogenous uridine and thymidine into the soluble pool. The transport process can be restored by supplementing the growth medium with cis-unsaturated fatty acids but not trans-unsaturated ones although the growth of the cells is resumed by supplementation with eithercis or trans-unsaturated fatty acids. However, supplementation withtrans, trans-unsaturated fatty acids leads to only partial recovery of the transport process. The rate of oxygen uptake is also affected in cells grown in the presence of thetrans-unsaturated fatty acids, elaidic acid and palmitelaidic acid. Analysis of cells grown under different fatty acid supplementation indicate that fatty acid composition of the cell membrane, especially the ratio of unsaturated to saturated fatty acids varies with temperature shift and supplementation of the growth media with fatty acids.

    • Effect ofcis andtrans unsaturated fatty acids on the transport properties ofSalmonella typhimurium

      J K Deb R Goyal M Chakravorty

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      The transport of α-methyl-D-glucoside and two aminoacids, L-phenylalanine and L-leucine by a temperature sensitive fatty acid requiring mutant ofSalmonella typhimurium was studied under conditions of supplementation withcis or trans-unsaturated fatty acids. The results of such experiments definitely establish a relationship between the fatty acids composition of the membrane and the transport property of the cells. Cells grown in the presence of trans-unsaturated fatty acids cannot transport so efficiently as compared to the cis-unsaturated fatty acid-grown cells except linolelaidic acid, atrans-trans-unsaturated fatty acid. Protein: phospholipid ratio of the membrane also varies significantly under such conditions. The affinity of L-phenylalanine transport carrier for the substrate changes remarkably in cells grown in the presence of differentcis or trans-unsaturated fatty acids and indicate the possible role of membrane lipids in membrane assembly as well as regulation of the activity of L-phenylalanine transport system.

    • Replication, maturation and physical mapping of bacteriophage MB78 genome

      Saeed A Khan S S Murty Manzoor A Zargar M Chakravorty

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      Bacteriophage MB78 is a virulent phage ofSalmonella typhimurium. The viral DNA is 42 kb in size and seems to be circularly permuted. We show that viral DNA replication is through concatemeric DNA formation which is subsequently converted into full length DNA through headful packaging. A restriction map of MB78 DNA for six restriction endonucleases e.g.BgIII,PvuII, ECORI, ClaI, SalI and SmaI has been constructed. The yield of certain fragments in less than molar amount is explained in terms of permutation and the headful mechanism of packaging. The packaging site (pac site) has been suggested.

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