Biomedical subjects
Publications and source records attributed to S Litvak.
Human platelets have two DNA polymerases. In the mitochondrial-free cytoplasm we have found a DNA polymerase gamma and another DNA polymerase very closely related to the polymerase alpha from animal cells. In the mitochondria only the gamma activity is present.
DNA polymerase gamma from purified nuclei of EMT-6 cells (mice) seems to be identical to the mitochondrial DNA polymerase from the same source following several criteria. These two enzyme activities are strongly inhibited by ethidium bromide and acriflavin, while proflavin, acridine orange, daunomycin and chloroquine inhibition is less pronounced. In the case of DNA polymerases alpha and beta very little inhibition by ethidium bromide was observed. Intercalation of this dye in a poly dA-dT 12-18 template-primer was studied spectrophotometrically under conditions similar to those in the in vitro DNA polymerase assay. The polymerase assay. The inhibition by this drug of the mitochondrial DNA polymerase gamma activity was shown to be competitive at varying concentrations of TTP while the inhibition was of the non-competitive type at different concentrations of poly dA-dT 12-18. We conclude that the drug, most probably in the intercalated form, is able to interact with the active site (s) of mitochondrial DNA polymerase.
The enzyme tRNA nucleotidyl transferase (EC 2.7.7.25) has been highly purified from whole adult houseflies. A molecular weight of 30 000 has been determined. The enzyme requires Mg2+ and tRNA deprived of the 3' terminal sequence CCA for activity in the incorporation of AMP and CMP onto the tRNA. UMP can be incorporated instead of CMP but the latter has a higher affinity than UMP as shown by competition experiments. A complex between the enzyme and tRNA has been shown by sucrose gradient centrifugation, nitrocellulose binding and protection by tRNA against enzyme denaturation at 50 degrees C. Comparative studies with tRNA nucleotidyl transferase purified from larvae, pupae and adult insects indicate that tRNA nucleotidyl transferase from these three developmental stages have the same molecular weight, sedimentation coefficient and optimum pH while the larval enzyme differs from the pupae and adult enzymes in the elution behaviour from a DEAE-cellulose column.
Ribonucleic acid from TMV and BMV can accept AMP and CMP when digested with VPD. This incorporation is catalyzed by E. coli and yeast tRNA nucleotidyl transferases. Complex formation is obtained between TYMV RNA and tRNA nucleotidyl transferase in sucrose gradients while TMV and BMV RNAs failed to form a complex in the same conditions. The affinity of the enzyme for viral RNAs is lower than the affinity for tRNA as shown by complex formation on nitrocellulose filters and competition with tRNA. Coat protein from TMV particles enhances AMP and CMP incorporation onto tRNA catalyzed by the E. coli tRNA nucleotidyl transferase.
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Two DNA polymerases have been purified from the 105,000 x g supernatant of ungerminated wheat. The purification stages included: high speed centrifugation, salt fractionation, DEAE-cellulose chromatography, Sephadex G-150 filtration and phosphocellulose chromatography. Several properties of the two enzyme (called A and B according to the order of elution from the phosphocellulose column) have been studied. Enzyme A has a sedimentation coefficient of about 7 S, utilizes activated DNA and synthetic polydeoxynucleotides as well as poly rA-dT12, while B has a sedimentation coefficient of about 6.2 and uses only activated DNA and synthetic polydeoxynucleotides as templates. Other parameters like KCl effect, MnCl2 effect, optimum pH, etc. Allow us to distinguish clearly between both DNA polymerases.
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Turnip yellow mosaic virus (TYMV) RNA treated with snake venom phosphodiesterase accepts cytidine 5'-monophosphate and adenosine 5'-monophosphate (AMP) when it is incubated in the presence of cytidine 5'-triphosphate (CTP), adenosine 5'-triphosphate, and Escherichia coli transfer RNA nucleotidyltransferase; untreated TYMV RNA accepts only AMP. When alpha (32)PCTP was used for terminal labeling, the nearest neighbor analyses and the anallyses after action of various nucleases showed that the sequence of five nucleotides at the 3' end of TYMV RNA is: pGpCpApCpC. A nuclease present in commerical preparations of snake venom phosphodiesterase leads to the fragmentation of TYMV RNA, the 3' end of which is found in a fragment having a sedimentation constant close to 5s.
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