DNA strand reassociation and polyribonucleotide binding in the African green monkey, Cercopithecus aethiops

Abstract

About 20% of the nuclear DNA from tissues and cultured cells of the African green monkey, Cercopithecus aethiops, consists of a homogeneous fraction that is comparable to mouse satellite DNA in the rapidity and precision with which the denatured DNA reassociates. Although this DNA, designated C. aethiops component α, shares several of the properties of mammalian satellite DNA's, it bands in CsCl at the same density (1.699 g/ml.) as the non-reassociating bulk DNA. Component α DNA comprises up to 75% of the DNA from nucleolar preparations from cultured C. aethiops kidney cells (BSC-1 and CV-1). In addition, CV-1 and primary C. aethiops kidney explants contain a heavy satellite (ϱ = 1.711 g/ml.) representing 5 to 7% of the total nucleolar DNA, which was not detected in similar preparations from BSC-1 cells. In alkaline CsCl component α separates into two populations of complementary strands. Neither the duplex molecule nor the separated single strands interact with the homopolyribonucleotides, poly U and poly G, under conditions in which the denatured bulk DNA interacts with both and increases markedly in density. On the other hand, the light strands, which band at a density of 1.757 g/ml. in alkaline CsCl, interact with the copolymer, poly (U,G) as does the bulk DNA. The heavy strands (ϱ = 1.764 g/ml. in alkaline CsCl) do not interact. Alkali-denatured nuclear DNA of C. aethiops cells elutes as three peaks and nucleolar DNA as one peak from methylated albumin kieselguhr chromatography columns with linear salt and pH elution gradients. The elution order could be correlated with the amounts of component α DNA in each fraction as well as the restriction in the ability to bind the polyribonucleotides. The complementary strands of component α could not be separated by this method, however. In the presence of Ag + or Hg 2+, component a bands in Cs 2SO 4 at a density different from the bulk DNA, although both fractions show the same density in CsCl or in Cs 2SO 4 in the absence of heavy metals and presumably have the same (G + C) content.