Showing papers by "David Baltimore published in 1966"

An Intermediate in the Synthesis of Poliovirus RNA.

Abstract: The pairwise complementarity of the nucleotide residues in nucleic acids provides a simple mechanism for the specification of the sequence of residues in a nucleic acid. A molecule with a given sequence will specify a molecule with a complementary sequence and, in turn, the complementary molecule can specify the sequence of the original one. In the case of single-stranded RNA viruses, it is thus likely that a strand of complementary RNA will be the intracellular template for the synthesis of viral RNA (the molecule which exists in mature particles). This argument is strengthened by the finding of double-stranded RNA in cells infected with single-stranded RNA viruses. The hypothesis that the complementary molecule of RNA, in a double-stranded RNA, is the template for viral RNA synthesis requires that there be a region of hydrogen bonding between the growing molecule of viral RNA and the complementary RNA. As the new chain of viral RNA elongates, either it displaces the viral strand of the double-stranded RNA or it is not hydrogen-bonded except in proximity to the growing point. In either case, the growing strand of viral RNA plus its template will form a complex which will be partially single- and partially double-stranded. Since more than one molecule of nascent viral RNA could be attached to one double-stranded molecule, such complexes might be fairly large and easily distinguishable from true double-stranded RNA by their content of single-stranded RNA. We shall present evidence in this paper for the existence of such a complex of single- and double-stranded RNA in cells infected with poliovirus. It is similar to a structure first identified in bacteria infected with an RNA bacteriophage which was named the replicative intermediate (RI). We shall retain this nomenclature.

The effect of HeLa cell cytoplasm on the rate of sedimentation of RNA

Abstract: Ordinarily, sedimentation analysis of RNA preparations is carried out in simple aqueous solutions. Recently, numerous investigators have carried out experiments where RNA's in cytoplasmic extracts from various types of cells have been analyzed by sedimentation through gradients of sucrose. The implicit assumption has been made that the presence of the cytoplasmic extract does not in itself affect the rate of sedimentation of the RNA. However, we have recently found that some component of HeLa cell cytoplasmic extracts causes a 1.5-2-fold increase in the sedimentation rate of a number of species of RNA. Since this result bears on the interpretation of many types of experiments, we will report the phenomenon at this time, even though we know little about its mechanism.