DNA-DEPENDENT SYNTHESIS OF RNA BY Escherichia coli RNA POLYMERASE: RELEASE AND REINITIATION OF RNA CHAINS FROM DNA TEMPLATES

RNA synthesis in an in vitro RNA polymerase system at low ionic strength soon ceases, due to inhibition by accumulated RNA. Measurement of RNA chain initiation by the incorporation of gamma-(32)P-ATP and GTP with native T2 or T4 DNA as template shows that only one RNA chain is formed per molecule of enzyme added. In contrast, when the polymerase reaction is carried out in 10 mM Mg(++) and 0.2 M KCl, RNA synthesis proceeds nearly linearly for hours, resulting in a marked increase in accumulated RNA. Incorporation of gamma-(32)P-ATP also proceeds throughout the course of the reaction and the number of chains initiated per molecule of enzyme is increased severalfold. Most RNA chains formed are released from the DNA template as free RNA. Polymerase is released also in this process and acting catalytically reinitiates new chains. Rifampicin inhibits initiation of RNA synthesis and also blocks reinitiation of RNA chains without affecting growth of RNA chains already initiated.     

THE UTILIZATION OF GENES FOR RIBOSOMAL RNA, 5S RNA, AND TRANSFER RNA IN LIVER CELLS OF ADULT RATS

The rates of synthesis of ribosomes, 5S RNA, and tRNA necessary to maintain the steady-state concentrations of these entities in liver cytoplasm of adult rats were determined. On the average, each liver cell in the adult rat synthesizes 650 ribosomes, 650 molecules of 5S RNA, and 11,000 molecules of tRNA each minute. The numbers of genes per liver cell for rRNA, 5S RNA, and tRNA were 330, 1660, and 13,000, respectively, as determined by RNA: DNA hybridization experiments. Thus, on the average, individual genes for rRNA, tRNA, and 5S RNA are transcribed twice a minute, once a minute, and once every 2.5 minutes, respectively, in the adult rat liver.     

ONCOGENES OF RNA TUMOR VIRUSES AS DETERMINANTS OF CANCER

Evidence from sero-epidemiological studies and from cell culture studies supports the hypothesis that the cells of many, and perhaps all, vertebrates contain information for producing C-type RNA viruses. It is postulated that the viral information (the virogene), including that portion responsible for transforming a normal cell into a tumor cell (the oncogene), is most commonly transmitted from animal to progeny animal and from cell to progeny cell in a covert form. Carcinogens, irradiation, and the normal aging process all favor the partial or complete activation of these genes. An understanding of how normal cells and normal animals prevent expression of endogenous viral information would appear to offer one of the best hopes for the control of naturally occurring cancers.     

INDUCTION OF INTERFERON BY PREPARATIONS OF SYNTHETIC SINGLE-STRANDED RNA

A study was undertaken to help determine whether synthetic nonbase-paired, single-stranded RNA as well as synthetic base-paired, double-stranded RNA could induce interferon. Synthetic polyriboinosinic acid and polyribocytidylic acid induced interferon and interferon-like resistance in several different cell culture systems. However, in the intact rabbit only the most active preparations of single-stranded RNA induced circulating interferon when injected intravenously. The induced interferon and antiviral effect in tissue culture and animals was shown to have characteristics of the interferon system. Contamination of the single-stranded synthetic RNA materials by small amounts of base-paired, double-stranded RNA was ruled out by failure to find sufficient heterologous nucleic acid bases by differential activities of single-stranded and double-stranded RNA's in different cell systems and by failure to detect double-stranded RNA in poly-rI upon chromatography on benzoylated DEAE-cellulose.