On the ribonucleic acid synthesized in a cell-free system of Escherichia coli

Genetic Code: Emergence of a Symmetrical Pattern

The triplets of nucleotides which apparently specify the detailed structure of proteins fall into a regular pattern: the 64 combinations of four nucleotides taken three at a time, are resolved into 32 pairs. The second member of each pair is identical with the first, except that in one position a purine is replaced by the other purine or a pyrimidine by the other pyrimidine. Almost all of the reported triplets fit into this pattern, and from it one can predict which amino acids will be found to correspond to the remaining 19 unidentified triplets. This pattern accounts for several of the observations concerning regularities in the data, partially determines the order of the nucleotides in each triplet, and suggests a structural basis for transfer RNA specificity.

THE SYNTHESIS OF RIBOSOMES BY A MUTANT OF ESCHERICHIA COLI

1. When the methionine-requiring mutant 58-161 of Escherichia coli was starved of methionine, ribonucleic acid was made in the absence of protein synthesis. 2. Most of this ribonucleic acid was similar to that found in ribosomes but was contained in particles differing from ribosomes both in sedimentation coefficient and in chromatographic behaviour on diethylaminoethylcellulose. 3. When methionine was added to a starved culture, the ribonucleic acid synthesized during starvation was almost completely undegraded as growth resumed. A transient loss of 5-10% could be largely attributed to breakdown of messenger ribonucleic acid accumulated during starvation. 4. After the addition of methionine, ribosomes were formed from the particles, and during this period preferential synthesis of ribosomal protein took place. 5. It is suggested that under these conditions the direct synthesis of ribosomes from the particles may occur.

TRANSLATIONAL CONTROL OF PROTEIN SYNTHESIS IN A CELL-FREE SYSTEM DIRECTED BY A POLYCISTRONIC VIRAL RNA

Observations with RNA isolated from the RNA virus indicate that regulation of protein synthesis occurs during translation. At least three electrophoretically separable proteins, one of which lacks histidine, appear as a result of adding purified viral RNA to a cell-free extract of Escherichia coli. This establishes that the RNA contains at least three cistrons. Comparison of the kinetics of appearance of the proteins that do and do not contain histidine reveals a control mechanism which determines the temporal order and the frequency of translation of each cistron. Such translational controls at the stage of message use provide additional devices for regulating protein synthesis which can supplement those functioning at the transcription step where genetic messages are produced.

The separation of ribonucleic acids from Escherichia coli on lysin-agarose

Lysine-agarose provides a simple means of separating RNA species of different moleecular weight. When RNA from Escherichia coli is added to a small column of lysine-agarose and elution is carried out at neutral pH with a shallow linear gradient of NaCl the RNA species are eluted according to size; 4S and 5S RNA species are completely separated and after a delay the 16S and 23S species are eluted as separate peaks. The process is very reproducible and the different species are eluted at a fixed salt concentration even when changes are made in the gradient, provided other conditions, under which the column is run remain constant.

Isolation and characterization of bacterial ribosomal RNA cistrons

The DNA sequences which code for ribosomal DNA have been isolated and purified. The technique used has general application for RNA:DNA hybridization studies and enables the isolation of any gene for which sufficient gene product can be obtained. Experiments with isolated ribosomal RNA cistrons demonstrated that (a) the majority of the ribosomal cistrons are similar to one another; (b) the cistrons which are similar to one another are virtually identical to one another; (c) ribosomal cistrons of different bacterial species are closely related to one another.

Studies on components of RNA in cardiac muscle with emphasis on the rapidly labeled 4 to 18 S fraction

Studies on RNA from cardiac muscle of rats were performed by labeling the RNA with 32 P, extracting it with phenol, and purifying it prior to fractionating and analyzing it on a sucrose density gradient. The major components of RNA found had sedimentation values of 28, 18, and 4 S. Early 32 P-labeled RNA ranged in size from 4 to > 45 S. Characterization of RNA from 4 to 18 S showed it to be more rapidly labeled and to have a higher turnover rate than 28 S RNA, to be located, at least in part, in the microsomes, and to have a base composition lower in guanine and cytosine content than 28 S RNA. Labeling of 4 to 18 S and 28 S RNA was equally inhibited by actinomycin. The possibility that 4 to 18 S RNA may represent a portion of messenger RNA in cardiac muscle is considered.

Replicating Form of a Single-Stranded DNA Virus: Isolation and Properties

The replicating form of single-stranded DNA virus has been isolated in pure form by chromatography on columns of methylated albumin. Its buoyant density in CsCl and "melting temperature" are characteristic of a double stranded DNA structure containing 43 percent guanine-cytosine. The nearest neighbors to uridylate were compared in the RNA synthesized when replicating-form DNA and mature single-stranded DNA were employed as templates in an in vitro system. The mature DNA component of the replicating duplex does not serve as the sole source of complementary RNA. The results agree best with the assumption that both strands of the replicating form function as templates. It is important to note that this is contrary to the situation found in the intact cell where only one of the two strands appears to be transcribed into message.