Effects of Polyinosinic Acid and Polycytidylic Acid on the Deoxyribonucleic Acid Template Activity of Isolated Nuclei and Soluble Chromatin from Rat Liver

Abstract

Abstract 1. Polyinosinic acid (poly(I)) is capable of releasing the DNA template restrictions of rat liver nuclei or soluble chromatin when assayed with Escherichia coli DNA polymerase. In contrast, polycytidylic acid (poly(C)) is completely ineffective. 2. The ability of poly(I) to release the DNA template restrictions is dependent on the size of the poly(I). Poly(I) with sedimentation values from 4.1 to 12.5 S are good template activators while an equivalent amount of the smaller poly(I) with an s20,w value of 2.5 is far less effective. In comparison, poly(C) with sedimentation values from 3.1 to 13.2 S are incapable of activating the template DNA of either rat liver nuclei or chromatin. 3. The similarity of the poly(I) effect on both isolated nuclei and soluble chromatin indicate that the specificity of the polymer for DNA template activation is not determined by its ability to pass through the nuclear membrane. 4. The double-stranded homopolymer pair poly(I)·poly(C) is completely ineffective in activating template DNA. Similarly, the nuclear template-activating ability of poly(I) can be totally inhibited if the bases of the poly(I) are methylated in the N-7 position. 5. Radioactive poly(I), but not radioactive poly(C), is capable of binding to isolated rat liver nuclei and soluble chromatin. Similarly, poly(I), but not poly(C), produced an optical clearing of nuclear suspensions when measured at A600 nm. This phenomenon was accompanied by a release of DNA from the nuclei. 6. Poly(I), and to a lesser extent poly(C), was able to protect high molecular weight DNA in nuclei from degradation when nuclear suspensions were incubated at 37° in the presence of 2.5 mm magnesium ion. 7. DNA template characteristics of calf thymus DNA could be completely inhibited by the addition of unfractionated calf thymus histones. Large sizes of poly(I) were specifically able to reactivate the template properties of these histoneinhibited DNA preparations. 8. These results indicate that the ability of specific polyribonucleotides to activate template DNA depends on several characteristics of the polymer including its composition, size, and secondary structure in solution.