• K. Dharmalingam

      Articles written in Journal of Genetics

    • Heat shock-induced relaxation of restriction enzyme specificity inEscherichia coli

      M. C. Raja K. Dharmalingam

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      Methylated and hydroxymethylated cytosine containing DNA was restricted by proteins encoded by themcrBC (rglB) loci ofE. coli. In vivo, RglB proteins recognize and cleave hmCT2 and hmCT4 DNAs at 30°C and 42°C but hmCT6 DNA was unaffected at both temperatures, However, cells carrying therglB genes cloned on pBR322 (pDSS17) did not restrict hmCT6 at 30°C, but hmCT6 DNA was cleaved efficiently at 42°C. Heat shock treatment for five minutes was enough to induce this promiscuity in recognition specificity. We call this activity RglB star. A single copy ofrglB located on the chromosome or cloned on a low copy vector pMU575 failed to show RglB star activity.De novo protein synthesis was not required for the manifestation of RglB star activity.

    • Isolation and characterization of stable mutants ofStreptomyces peucetius defective in daunorubicin biosynthesis

      K. S. Vetrivel K. Dharmalingam

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      Daunorubicin and its derivative doxorubicin are antitumour anthracycline antibiotics produced byStreptomyces peucetius. In this study we report isolation of stable mutants ofS. peucetius blocked in different steps of the daunorubicin biosynthesis pathway. Mutants were screened on the basis of colony colour since producer strains are distinctively coloured on agar plates. Different mutants showed accumulation of aklaviketone, ε-rhodomycinone, maggiemycin or 13-dihydrocarminomycin in their culture filtrates. These results indicate that the mutations in these isolates affect steps catalysed bydnrE (mutants SPAK and SPMAG),dnrS (SPFS and SPRHO) anddoxA (SPDHC) gene products.

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