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The two types of 30-S · 50-S couples described in the preceding paper, differ markedly in their sensitivity to hydrostatic pressure evoked during centrifugation in sucrose gradients. The sedimentation coefficient of about 60 S recorded with couples formed from native subunits is only apparent, the real a value being 70 S. The latter couples can be stabilized against pressure-induced dissociation by bound tRNA. On the other hand this binding renders couples formed from derived subunits more sensitive to this dissociation. As the factor determining this intriguing difference in pressure sensitivity lies in the 50-S subunit, a comparative analysis of a number of ribosomal constituents has been performed for native and derived 50-S particles. No qualitative differences in the proteins L1–L34 have been detected. Quantitative differences cannot yet be excluded. It is considered unlikely that differences in rRNAs or low-molecular-weight components arc responsible for the distinct association behaviour. Partial reconstitution of ribosomal γ-cores and split proteins detached by CsCl reveals that the determinant factor is located in the core particles. This suggests that native and derived 50-S subunits do not differ in conformation only. The possibility may be envisaged therefore, that the two types of 50-S differ in a ribosomal protein. [ABSTRACT FROM AUTHOR]

In this paper an efficient procedure is described for the isolation of polysomes from tissue culture cells. optimal yields, especially of the heavier classes of polysomes can only be obtained at a rather high KCl concentration in the presence of nonionic detergent. Evidence is provided that the lower polysomal yield after extraction at low salt concentration is not due to breakdown of the polysomes by RNAase. Furthermore, the yield of polysomes is pH dependent only at low salt concentration, while at high salt concentration no influence of the pH is observed. Refreshing of growth medium several hours before harvesting the cells, increases the ratio of polysomes to 80 S monomers. [ABSTRACT FROM AUTHOR]

1. The distribution of ribosomal particles between the soluble and membrane fractions of exponential-phase cells of Bacillus licheniformis was studied. The cells were very gently lysed by a combined treatment with lysozyme and Brij 58 in 10 mM. Tris-buffer, pH 7.6, with 60 mM K+, 10 mM Mg2+, 0.5 mM spermine and 0.75 mM spermidine. The proportion of the ribosomal material present in the membrane fraction was estimated after solubilization of the membranes by the combined action of Brij 58, deoxyribonuclease and lipase. 2. Under these conditions of lysis 96% of the total ribosomal material, consisting of subunits (12%) monosomes (20%) and polyribosomes (68%) and most of the cellular DNA, is found to be membrane-bound. 3. In the soluble fraction, containing only 4% of the total cellular amount of the ribosomal material, only subunits and 70S particles and no polyribosomes are found. 4. DNA does not seem to be involved in the binding of the ribosomal material to the membranes. 5. The results will be discussed considering the question of whether the distribution described in this paper represents the true distribution in vivo of ribosomes. [ABSTRACT FROM AUTHOR]