Synthesis of ribonucleic acid by mengovirus-induced RNA polymerase in vitro: nature of products and of RNase-resistant intermediate

Effect of ultraviolet light on mengovirus: formation of uracil dimers, instability and degradation of capsid, and covalent linkage of protein to viral RNA

UV irradiation of purified mengovirus resulted in a very rapid inactivation of the infectivity of the virions (D(37) [37% survival dose] = 700 ergs/mm(2)) which correlated in time with the formation of uracil dimers in the viral RNA. During the first 2 min of irradiation, an average of 1.7 uracil dimers were formed per PFU of virus inactivated. Hemagglutination activity of the virions began to decrease only after a lag period of about 5 min and at a much lower rate (D(37) = 84,000 ergs/mm(2)). This decrease coincided in time with the appearance of altered proteins in the capsid and a structural change in the capsid. Although 10- to 20-min irradiated virions appeared intact in the electron microscope and sedimented at 150S in sucrose density gradients, the RNA of the virions became accessible to RNase and extractable by low concentrations of sodium dodecyl sulfate, and the virions broke down upon equilibrium centrifugation in CsCl gradients. During longer periods of irradiation (30 to 60 min), a progressively greater proportion of the virions were converted to 14S protein particles and 80S ribonucleoprotein particles composed of intact viral RNA and about 30% of the capsid proteins, alpha, beta, and gamma. Empty capsids were not detectable at any time during 60 min of irradiation, by which time disruption of the virions was complete. Irradiation of complete virions also resulted in an increased sedimentation rate of the viral RNA and in the covalent linkage to the viral RNA of about 1% of the total capsid protein in the form of heterogeneous low-molecular-weight polypeptides. The two observations seem to be causally related, since irradiation of isolated viral RNA did not result in an increase in sedimentation rate of the RNA, even though uracil dimer formation in viral RNA occurred at about the same rate and to the same extent whether intact virions or viral RNA were irradiated.

Ribonucleic acid and protein synthesis during germination of Myxococcus xanthus myxospores

Ribonucleic acid (RNA) and protein synthesis during myxospore germination were examined. When RNA synthesis was inhibited more than 90% by either actinomycin D (Act D) or rifampin, germination was prevented. The data were consistent with the interpretation that rifampin did not interfere with protein synthesis in any way other than by inhibition of messenger RNA formation. Act D concentrations as high as 20 mug/ml did not totally inhibit RNA synthesis. In the presence of 8 mug of Act D/ml, germinating myxospores synthesized transfer RNA, 16S RNA, and 23S RNA. Evidence was presented which indicated that messenger RNA was also synthesized early in the germination period both in the presence and absence of 8 mug of Act D/ml. One explanation for the escape synthesis of RNA in germinating myxospores is that Act D exerts a differential effect on the transcription of larger versus smaller cistrons, the latter having a lower probability of binding Act D. We have found that in the presence of 8 mug of Act D/ml, escape RNA synthesis in myxospores was 25% for 23S RNA, 55% for 16S RNA, and more than 90% for 4S RNA. We have shown that germination of myxospores requires both RNA and protein synthesis during the first 25 to 35 min in germination medium. This finding does not support the earlier suggestion by Ramsey and Dworkin that a stable germination messenger RNA is required for germination of the myxospores of Myxococcus xanthus.

Nucleotide pools in Novikoff rat hepatoma cells growing in suspension culture. 3. Effects of nucleosides in medium on levels of nucleotides in separate nucleotide pools for nuclear and cytoplasmic RNA synthesis

This study was undertaken to measure the absolute levels of nucleoside pools in Novikoff rat hepatoma cells (subline N1S1-67) during growth in suspension culture in the presence of high concentrations of various nucleosides in the medium, and to obtain further evidence for the compartmentalization of the nucleotides in independent cytoplasmic and nuclear pools. The levels of nucleotide pools were measured by growing the cells in medium supplemented with inorganic phosphate-(32)P. The nucleotide pool levels (mostly in the form of triphosphates) ranged from about 1 nmole of cytidine nucleotides to 8 nmole of adenosine nucleotides per 10(6) cells. The presence of 1 mM uridine, cytidine, guanosine, or adenosine in the medium resulted in marked increases in the intracellular levels of the corresponding nucleoside phosphates of at least 3-4 nmole/1O(6) cells. These increases were partially compensated for by decreases in the levels of other nucleotides. Evidence is presented to indicate that it is the cytoplasmic pool that expands during incubation with high concentrations of nucleosides in the medium, whereas the nuclear pool remains constant and very small in size. Preincubation of cells with 1 mM uridine-(3)H for 5.5 hr, which resulted in a threefold increase in the total intracellular level of uridine nucleotides, had no effect on the subsequent incorporation of uridine-(14)C into cellular nucleic acids in the nucleus, whether present at a 1 microM or 1 mM concentration in the medium. In contrast, the incorporation of uridine-(14)C into cytoplasmic viral-specific RNA by mengovirus-infected Novikoff cells was reduced 60-70% as a result of preincubation of the cells with high concentrations of uridine-(3)H. Further, within 1-2 min upon addition of 2.5 or 6.5 microM(3)H-labeled uridine, cytidine, adenosine, guanosine, or inosine to cultures of Novikoff rat hepatoma cells, the incorporation of label into nucleic acids reached a constant and maximum rate, in spite of the presence of high intracellular concentrations (0.4-3 mM) of the corresponding unlabeled nucleoside triphosphates. Marked differences were also observed in the relative incorporation of the various nucleosides into the different nucleotides of the acid-soluble pool, and of mengovirus RNA and cellular RNA.

Effect of mengovirus replication on choline metabolism and membrane formation in novikoff hepatoma cells

Infection of Novikoff rat hepatoma cells (subline NlSL-67) with mengovirus resulted in a two- to threefold increase in the rate of choline incorporation into membrane phosphatidylcholine at about 3 hr after infection, without affecting the rate of transport of choline into the cell or its phosphorylation. The time course of virus-stimulated phosphatidylcholine synthesis was compared with the time courses of other virus-induced processes during a single cycle of replication. The formation of viral ribonucleic acid (RNA) polymerase and of viral RNA commenced about 1 hr earlier than the virus-stimulated choline incorporation. Further, isopycnic centrifugation of cytoplasmic extracts indicated that the excess of phosphatidylcholine synthesized by infected cells is not located in the membrane structures associated with the viral RNA replication complex, but with structures of a lower density (1.08 to 1.14 g/cc). These membrane structures probably represent the smooth vesicles which accumulate in the cytoplasm of infected cells during the period of increased phosphatidylcholine synthesis between 3 and 5 hr after infection. They are formed with both newly synthesized phosphatidylcholine and phosphatidylcholine present prior to infection. However, concomitant protein synthesis is not required for the stimulated synthesis of membranes; the effect was not inhibited by treating the cells with inhibitors of protein synthesis at 3 hr after infection, although virus production was inhibited about 90% and virus-induced cell degeneration was markedly reduced and delayed. Production of mature virus began normally at about the same time as the stimulation of phosphatidylcholine synthesis. Treatment of infected cells with puromycin at 2 hr, on the other hand, completely inhibited the stimulation of phosphatidylcholine synthesis.

In vitro product of a ribonucleic acid polymerase induced by influenza virus

The ribonucleic acid (RNA)-dependent RNA polymerase induced in the microsomal fraction of cells infected with influenza virus synthesized a mixture of single-and double-stranded RNA in vitro. The single-stranded RNA sedimented mainly in the 8S region on sucrose density gradients, with a smaller proportion of the RNA sedimenting at 18S. This sedimentation pattern corresponds closely to that of incomplete influenza virus RNA. The double-stranded RNA formed in vitro sedimented at 11S, but molecules which may be replicative intermediate, sedimenting at 14 to 20S, were also detected in the in vitro reaction product. Similar species of RNA were detected in vivo by pulse-labeling infected cells at the time of polymerase harvest, but the proportion of each RNA species was different, most of the RNA being single-stranded and sedimenting in the 18S region. An 11S double-stranded RNA was also synthesized in vivo. Pulse chase analysis of the double-stranded RNA synthesized in vitro showed that most is stable, and only a small proportion turns over during the reaction. A proportion of the RNA formed in vitro could be annealed to RNA formed in infected cells and to RNA extracted from purified virus.

Sindbis virus-induced viral ribonucleic acid polymerase

A cytoplasmic structure containing the viral ribonucleic acid (RNA) polymerase has been isolated by sucrose density centrifugation from cells infected with Sindbis virus. Uninfected cells did not contain any such structure. Preliminary experiments indicated that the structure may be associated with membranes. This structure incorporated (3)H-guanosine triphosphate in vitro in the absence of added template. The RNA synthesized in vitro by the enzyme consisted of single-stranded 40S RNA, the ribonuclease-resistant replicative form, and possibly the replicative intermediate form of viral RNA. The products formed in vitro by the enzyme are identical in sedimentation rates to those formed in the infected cells in vivo.

Encephalomyocarditis virus ribonucleic acid polymerase associated with 150S cytoplasmic particles

Cytoplasmic particles which sedimented at 150S were the smallest structures containing detectable viral ribonucleic acid polymerase in mouse cells infected with encephalomyocarditis virus.

In vitro synthesis of poliovirus ribonucleic acid: role of the replicative intermediate

Poliovirus ribonucleic acid (RNA) polymerase crude extracts could be stored frozen in liquid nitrogen without loss of activity or specificity. The major in vitro product of these extracts was viral single-stranded RNA. However, after short periods of incubation with radioactive nucleoside triphosphates, most of the incorporated label was found in replicative intermediate. When excess unlabeled nucleoside triphosphate was added, the label was displaced from the replicative intermediate and accumulated as viral RNA. It is concluded from this experiment that the replicative intermediate is the precursor to viral RNA. In addition, some of the label was chased into double-stranded RNA. The implications of this finding are discussed.