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The photodynamic inactivation of nucleic acids with pyronin, methylene blue, thiopyronin and furocoumarines has been studied. The template efficiency of DNA in RNA-Polymerase reaction was found to be decreased after the treatment of DNA with these compounds. However, the magnitude of their inhibiting capacity varied from one compound to the other. Psoralen and thiopyronin were found to be the most active inhibitors followed by xanthotoxin and methylene blue respectively. At a lower temperature the inhibiting capacity of thiopyronin was considerably decreased but that of psoralen remained nearly unaffected. We have also tried to show evidence for a complimentary code in t-RNA through a specific destruction of guanine with thiopyronin.
The effect of NNMG on the template activities of different polynucleotides (polyuridylic acid, polycytidylic acid, polyadenylic acid and copolymer of adenylic and guanylic acid 5,5:1) and t-RNS was studied. The maximum inhibition of the messenger activity was found for poly-C, followed by poly-Α and poly-U. The acceptor activity of t-RNA was found to be inhibited by NNMG: maximum for proline, followed by serine, leucine, phenylalanine and lysine. The mechanism of these inhibitions was studied using NNMG radioactively labelled on the methyl group. Different amounts of radioactivity were found in the various polynucleotides and t-RNS.
The non-specific inhibition of the poly U directed polymerisation of phenylalanine through polyanions was studied. This inhibition was found to be in order as follows: dextransulfate, polyethylensulfate, heparine, ribosomal RNA and alginate. It was found that poly A, poly AP and poly AG cause a specific inhibition of the poly U directed synthesis of polyphenylalanine. Poly AG and poly AP, but not poly A were found to inhibit the poly C directed polymerisation of proline as well. The mechanism of these two types of inhibition caused by polyanions has been discussed.
A study on the effect of UV-irradiated polyuridylic acid on the incorporation of phenylalanine into the polypeptide precipitable through trichloroacetic acid, in a cell-free system from E. coli was made. Attempts were made to reactivate the UV-inactivated polyuridylic acid through hydrogen peroxide, uranyl acetate and visible light. We could show that polyuridylic acid irradiated at a dose of 1.2 ×105 ergs/mm2 could be completely reactivated, while the one irradiated at a higher dose of 2.4 ×105 ergs/mm2 could not be completely reactivated under the conditions of our experiment. We have studied the effects of hydrogen peroxide and uranyl acetate on UV-irradiated polyuridylic acid chemically as well. Our results altogether show that the photoreactivating effect of uranyl acetate and hydrogen peroxide is due to their ability to split the uracil dimers formed during UV-irradiation.