Association of nascent polypeptide and transfer ribonucleic acid with 30S ribosomal subunits

1. Crude extracts of Escherichia coli programmed in protein synthesis by endogenous mRNA have incorporated amino acids into protein. Analysis of such extracts by sucrose-gradient centrifugation in low Mg(2+) concentration has revealed that 30S ribosomal subunits carry associated radioactive material of which a considerable proportion can be removed from ribosomes by treatment of pre-labelled extracts with puromycin. 2. Gradient analyses of incorporations carried out in the additional presence of added (32)P-labelled tRNA have indicated that tRNA sediments in the regions of the newly synthesized nascent protein and that both labels are associated with all ribosomal components detected on the gradients under the experimental conditions employed. 3. 30S ribosomal subunits carrying both (32)P and (14)C labels have been isolated, disrupted with sodium dodecyl sulphate, and analysed by chromatography on Sephadex G-200 columns. Both labels elute closely together and well away from a tRNA marker analysed under identical conditions. 4. It is proposed that 30S ribosomal subunits, isolated from extracts which have synthesized nascent peptides under the direction of endogenous mRNA, carry associated peptidyl-tRNA.

Association of nascent polypeptide with 30S ribosomal subunits

1. Crude extracts of Escherichia coli were used to synthesize nascent peptides under the direction of endogenous mRNA and in the presence of radioactive amino acids. Analysis of such extracts by sucrose-gradient centrifugation in low Mg(2+) concentration has shown that after 2min of incubation approximately 14% of the total labelled protein recovered on the gradient, in association with whole ribosomes, sediments with 30S ribosomal subunits; this value rises to approximately 24% after 30min of incubation. The labelled protein associated with 30S ribosomal subunits is insoluble in hot trichloroacetic acid. 2. Similar results were also obtained in extracts that synthesized polypeptides under the direction of either of the synthetic polyribonucleotides poly(A) or poly(A,G,C,U). In contrast, however, analysis of crude extracts programmed in protein synthesis by poly(U) has indicated that under these conditions 30S ribosomal subunits have no associated polyphenylalanine; similarly there is little associated peptide after programming of extracts by poly(U,C).

Nonequilibrium Thermodynamics in Chemical Kinetics

The description of chemical reaction rates, in terms of the language of nonequilibrium thermodynamics, is compared with the conventional language of chemical kinetics. It is concluded that the formalism of nonequilibrium thermodynamics possesses considerable disadvantages, even in the regime where the rate is a linear function of affinity; this conclusion also holds for cases where chemical rates are coupled to diffusion processes. Some of the difficulties involved are illustrated using the experimental data of Nebeker and Pings (28).

Individual differences in anagram-solving ability

Anagram solution was, as expected, significantly correlated with level of vocabulary ( r = .29), but, while high anagram scores are associated with high vocabulary, low anagram scores are as often associated with high as with low vocabulary. MMPI measures of Anxiety and Repression were unrelated to anagram solution. In a second study, as predicted, Mednick's RAT, the Gottschaldt Figures Test and an incidental recall measure were significantly correlated with anagram solution ( r = .43, .40, and .31, respectively, multiple R = .55), but the Stroop test, an incidental recognition measure and digit span measures were not. Two factors apparently underlie anagram solving ability—an adequate level of familiarity with words and the ability to shift attention in a directed but flexible manner.