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PubMed1961

Studies of E. coli ribosomal RNA and its degradation products.

The RNA of E. coli ribosomes has been extracted by the phenol method. The 70S ribosomes contain RNA molecules of 28 and 18S almost exclusively. When the 70S ribosomes are dissociated to 30 and 50S ribosomes the former contain only the 18S RNA and the latter a mixture of 28 and 18S RNA. There are also present, however, small quantities of ribosomal RNA having sedimentation coefficients of between 4 and 8S. These small molecules are particularly abundant in the smaller ribosomes present in the cell extract and account for most of the RNA of 20S ribosomes.In addition it has proved possible to degrade the large molecules of RNA to a series of smaller molecules. Removal of magnesium ions from the growing cell, extensive dialysis of the RNA against a buffer of low ionic strength, and heating all resulted in such degradation. Three degradation products were observed having sedimentation coefficients of about 13.1S, 8.8S, and 4.4S. The integral sedimentation distributions of these preparations suggest a high degree of homogeneity among the molecules of each of the three classes. The three sizes seem to result from sequential breaks in the molecules since the proportion of smaller molecules increases with time of treatment.The molecular weights of the 8.8S and 4.4S molecules have been estimated as 144,000 +/- 4,900 and 29,200 +/- 1,200 respectively by the Archibald method.

Escherichia coli↗
PubMed1961

A comparison of the native and derived 30S and 50S ribosomes of Escherichia coli.

Four types of ribosomes occurring in E. coli have been separated by sucrose gradient centrifugation. These are the 30S and 50S particles occurring in E. coli extracts (native particles), and the 30S and 50S particles which are the subunits of 70S ribosomes (derived particles). Two criteria were used in comparing these particles: (1) The type of RNA contained in each, as determined by sedimentation velocity in the analytical ultracentrifuge. (2) The ability of mixtures of 30S and 50S ribosomes (derived 30S + derived 50S, native 30S + native 50S) to undergo the reaction: [Formula: see text] Native and derived 30S particles were found to contain 16S RNA. Derived 50S particles contained 23S RNA and a small amount of 15 to 20S RNA, whereas native 50S ribosomes contained only 16S RNA. Derived 30S and 50S particles combined to form 70S particles. However, under identical conditions, native 30S and 50S particles did not form 70S ribosomes.

Escherichia coli↗
PubMed1961

The structure of high molecular weight ribonucleic acid in solution. A smallangle x-ray scattering study.

Small-angle x-ray scattering studies on an absolute scale have been carried out on isotropic solutions of high molecular weight RNA obtained from ascites tumor cells, E. coli, and yeast. It was found that in all three cases the RNA is composed of short rigid rods (50 to 150A in length) joined by small flexible regions. The rods account for almost the entire structure (at least 90 per cent); their radius of gyration about the axis and their mass per unit length are similar to those of DNA, suggesting a double-stranded helical structure. The rods are joined in an array forming the compact RNA molecule. On thermal degradation, the molecular superstructure disappears while the rods persist.

Escherichia coli↗
PubMed1962

Size distribution of "informational" RNA.

Previous investigations suggested that the size of "informational" or "messenger" RNA was confined to sedimentation rates lying between 8 and 14S. These involved procedures permitting extended contact of the RNA with enzymatically active extracts. The present study re-examined the size distribution of T2-complementary RNA isolated by a method which minimized enzymatic degradation. A much greater diversity in size distribution (4S to 25S) was observed. Experiments are described indicating that 8 to 12S informational RNA does not readily attach to the 16S and 23S ribosomal components under the conditions used for sedimentation analysis.

Escherichia coli↗