title: The deoxyribonucleic acid polymerases from the diatom Cylindrotheca fusiformis. Subcellular distribution, exonuclease activity and heterogeneity of the enzymes.
abstract: Four DNA polymerases from the marine diatom Cylindrotheca fusiformis, polymerases A, B, C and D, were further differentiated by their subcellular localization, presence of deoxyribonuclease activity, apparent heterogeneity and molecular weights. Polymerases A, B and D occur in significant amounts in the soluble fraction, suggesting that they were originally localized in the nuclei, whereas polymerase C predominates in the chloroplasts. A mitochondrial DNA polymerase was also isolated and characterized by ion-exchange chromatography. Polymerase D has an associated nuclease activity which prefers denatured DNA and Mg2+, and has a pH optimum higher than that for polymerase activity. Co-elution from a DEAE-Sephadex column and co-sedimentation in glycerol density gradients of deoxyribonuclease and polymerase D activity suggest a molecular association. Polymerases A, B and C are devoid of nuclease activity. Glycerol-gradient-sedimentation analysis showed that all DNA polymerase fractions are heterogeneous at low ionic strengths, with the appearance of a single homogeneous activity of 0.5M-KCl. Estimated molecular weights of 100000, 82000 and 120000 for polymerases A, B and C respectively were obtained from sedimentation analysis and gel filtration. Polymerase D was estimated to have a molecular weight of about 100000 as determined by sedimentation analysis alone.
mesh_terms: D002499:Centrifugation, Density Gradient; D002736:Chloroplasts / Q000201:enzymology; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism*; D003851:Deoxyribonucleases / Q000378:metabolism; D056890:Eukaryota / Q000201:enzymology*; D005092:Exonucleases / Q000378:metabolism; D008928:Mitochondria / Q000201:enzymology; D008970:Molecular Weight
chemical_list: D004259:DNA-Directed DNA Polymerase; D003851:Deoxyribonucleases; D005092:Exonucleases