In vitro translation of multistranded RNA from Escherichia coli infected by bacteriophage f-2

Viral RNAs associated with ribosomes in Sindbis virus-infected HeLa cells

Virus specific RNA ribosome complexes were isolated by sucrose density gradient centrifugation of cytoplasmic extracts from HeLa cells infected at 42 C with an RNA(+) mutant (ts2) of Sindbis virus. Viral RNA-ribosome complexes were accumulated by infected cells treated with sodium fluoride and cycloheximide. The RNA-ribosome complexes were characterized by (i) their sensitivity to the action of ribonuclease or ethylenediaminetetraacetic acid, (ii) their density in cesium chloride gradients, and (iii) presence of host ribosomes and viral RNAs. The viral RNAs were isolated and characterized. The results showed that two species of single-stranded RNAs (a 28s and 18 to 15s species) were associated with the complexes. Base composition analysis of the viral RNAs indicated that both species had a higher adenine content than the 42s or 26s forms of viral RNAs. The RNAs associated with the ribosome complexes were virus specific since they annealed with denatured double-stranded RNAs from the infected cells. Little or no 42S RNA was associated with the RNA-ribosome complexes. The results suggest that the 28s and 18 to 15s forms of RNAs may represent viral messenger RNAs.

Double-stranded RNA as an inhibitor of protein synthesis and as a substrate for a nuclease in extracts of Krebs II ascites cells

Concentrations of double-stranded RNA above about 0.1 mug/ml inhibit translation of encephalo-myocarditis viral RNA and mouse globin messenger RNA in extracts of Krebs II ascites cells. Protein synthesis initially proceeds at the control rate, then abruptly shuts off in a manner similar to that observed in reticulocyte lysates [Hunt, T. & Ehrenfeld, E. (1971) Nature New Biol. 230, 91-94]. Substantially higher concentrations of double-stranded RNA are required to give this effect in ascites extracts. Subcellular fractions of Krebs II ascites cells contain a nucleolytic activity capable of digesting several natural and synthetic double-stranded RNAs. This nuclease is most active under conditions of protein synthesis, and part of the activity remains associated with ribosomes upon sedimentation. It is probably because of digestion of double-stranded RNA by this nuclease that higher concentrations of double-stranded RNA are required for inhibition of protein synthesis in Krebs cell extracts than in reticulocyte lysates.

Assay for secondary structure in ribonucleic acid

A chromatographic procedure is described which can discriminate among single-stranded ribonucleic acid (RNA) molecules in solution on the basis of the extent of their secondary structure. The assay is effected through chromatography at different temperatures with columns of cellulose CF-11. When Sindbis virus RNA is chromatographed in this system, the ratio of the amounts of RNA eluting in the single-stranded peak to those eluting in the double-stranded peak increases at higher temperatures, presumably a measure of the relative amounts of Sindbis virus RNA secondary structure at different temperatures. With this assay, Sindbis virus RNA, phage f2 RNA, and polyuridylate have been found to have different amounts of secondary structure.

Polysomal localization of R17 bacteriophage-specific protein synthesis

Synthesis of viral ribonucleic acid (RNA) polymerase, maturation protein, and coat protein in Escherichia coli infected with bacteriophage R17 occurs mainly on polysomes containing four or more ribosomes. The 30S ribosomal subunits through trimer-size polysomes, which are associated with all of the R17-specific proteins and are predominant in the infected cell, synthesize only coat protein. These structures may accumulate as products derived from larger polysomes as a result of failure in the release of nascent polypeptides after termination of chain growth. Appreciable amounts of viral coat protein remain attached to ribosomes and polysomes during R17 bacteriophage replication, supporting the hypothesis of the repressor role of this protein. The time course of synthesis of virus-specific proteins obtained from the polysomes of infected cells demonstrated regulated R17 messenger RNA translation consistent with the idea that coat protein is preferentially synthesized whereas the synthesis of noncoat proteins is suppressed.

The action of mono- and di-functional sulphur mustards on the ribonucleic acid-containing bacteriophage mu2

Bacteriophage mu2 is inactivated by both mono- and di-functional sulphur mustards at relatively low extents of alkylation. No degradation of alkylated RNA was detected. Cross-linking of RNA to protein was observed with the difunctional agent, but this reaction was only a minor contribution to the inactivation. Analyses of the reaction products in bacteriophage RNA showed that, at the mean lethal doses, more than one mono-alkylation of guanine had occurred but the sum total of other types of RNA alkylation was close to a single event. The results therefore suggest that inactivation results from the mono-alkylation of adenine or cytosine. In experiments with the difunctional agent cross-linking of RNA bases or of RNA to protein also prevented replication, the existence of these reactions accounting for the greater sensitivity of the bacteriophage to this agent.

Structure of the poly(G) polymerase component of the bacteriophage f2 replicase

A rifampicin-resistant poly(G) polymerase has been purified from f2 sus 11-infected cells. The poly(G) polymerase is believed to represent part of the f2 replicase on the basis of several criteria. It is present only in infected cells and shares the characteristic rifampicin resistance of crude f2 replicase activity. Partially purified poly(G) polymerase preparations exhibit replicase activity, synthesizing f2 "lus"strand RNA from denatured, partially double-stranded f2 RNA template. Highly purified poly(G) polymerase preparations, although lacking replicase activity, contain a protein which is electrophoretically identical to the protein product of the viral replicase cistron.

Messenger characteristics of nascent bacteriophage RNA

The proteins initiated in vitro by nascent bacteriophage f2 RNA strands attached to isolated replicating structures have been analyzed. The observations confirm that coat protein is the major product initiated and completed. Nascent strands direct the initiation of viral maturation protein in amounts similar to the maximum levels observed in vivo; this synthesis is independent of translation of the coat protein gene. However, only a fraction of these maturation protein molecules initiated in vitro is completed. Nascent RNA molecules also direct the initiation of appreciable amounts of viral RNA polymerase protein, very little of which is completed. Certain constraints on the in vitro translation of the polymerase gene from single-stranded RNA appear to be relaxed in the nascent strands, as indicated by the reduced effect of a polar amber mutation in the coat cistron upon polymerase protein initiation from nascent RNA.

Self-assembly of Q-beta and MS2 phage particles: possible function of initiation complexes

Four kinds of particles were reconstituted with RNA and protein from the genetically unrelated bacteriophages Qbeta and MS2, namely, two homologous and two heterologous, with respect to RNA and protein. However, once Qbeta RNA (or MS2 RNA) reacted with a few molecules of either Qbeta or MS2 protein to form a nucleoprotein complex (initiation complex), it formed a phagelike particle only with subsequent addition of the same protein.