title: Two ribonucleases H from cultured plant cells.
abstract: Two forms of enzyme with ribonuclease H (RNase H) [EC 3.1.4.34] activities, have been partially purified from cultured plant cells, strain GD-2, derived from carrot root. One is an Mn2+-dependent RNase H, and the second is an Mg2+-dependent RNase H. These enzymes degrade RNA specifically in RNA-DNA hybrid structures. They were eluted at around 0.2 M and 0.4 M potassium chloride in phosphocellulose chromatography, and were further purified using blue Sepharose. Mg2+-dependent RNase H exhibits maximal activity at pH 9.0, and requires 10 to 15 mM Mg2+ for maximal activity, whereas the Mn2+-dependent enzyme is most active at pH 8.0, is maximally active at an Mn2+ concentration of 0.4 mM, and has some activity with Mg2+. Both enzymes require a sulfhydryl reagent for maximal activity. The enzymes liberate a mixture of oligonucleotides with 5'-phosphate and 3'-hydroxyl termini. The apparent molecular weight of the Mg2+-dependent RNase H was estimated to 18--20 X 10(4) and that of the Mn 2+- dependent RNase H was estimated to be 14 x 10(4) by gel filtration.
mesh_terms: D002478:Cells, Cultured; D004720:Endonucleases / Q000302:isolation & purification / Q000378:metabolism*; D007700:Kinetics; D008970:Molecular Weight; D010944:Plants / Q000201:enzymology*; D012260:Ribonucleases / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D004720:Endonucleases; D012260:Ribonucleases