ABSTRACT
Variant human fibroblast substrains, resistant to a cytotoxic human isoantiserum, were isolated from sensitive strains by repeated exposure to isoantiserum and rabbit complement. The resistant phenotype was stable, apparently occurred at low frequency, and was associated with loss of surface isoantigens.
Subject(s)
Diploidy , Fibroblasts/immunology , Isoantigens/isolation & purification , Animals , Complement System Proteins , Culture Techniques , Humans , Immune Sera , RabbitsABSTRACT
Four peaks of DNA-directed RNA polymerase activity are resolved by salt gradient elution of a sonicated yeast cell extract on DEAE-Sephadex. The enzymes, which are named IA, IB, II, and III in order of elution, all appear to come from cell nuclei. Only enzyme II is sensitive to alpha-amanitin. All enzymes are more active with Mn(++) than with Mg(++) as divalent ion. Enzymes IB and II have salt optima in the range 0.05-0.10 M (NH(4))(2)SO(4), whereas enzyme III is maximally active at 0.20-0.25 M (NH(4))(2)SO(4). With optimal salt concentration and saturating DNA, the template preference ratio, activity on native calfthymus DNA divided by activity on denatured calf-thymus DNA, is 2.2 for IB, 0.4 for II, and 3.5 for III. None of the yeast polymerases was inhibited by rifamycin SV. Rifamycin AF/013 effectively inhibited polymerases IB, II, and III.