Role of tissue specific factors in the translation of brain messenger ribonucleic acids in vitro

Isolation of free and membrane-bound polysomes and mRNA highly active in translation and reverse transcription from small discrete regions of rat brain

A procedure is described for the preparation of total polysomes, membrane-bound and free polysomes and polysomal mRNA from as little as 5 mg or less of brain tissue. These preparations were highly active when tested for translation and reverse transcription in vitro. Using this method, polysomes and mRNA from rat cerebral cortex, cerebellum, hippocampus and hypothalamus were compared. The results showed that membrane-bound polysomes were more active than free polysomes in protein synthesis. The activities of polysomes and mRNA for protein and cDNA synthesis were dependent on the specific brain structures from which they were obtained. Polysomes from cerebellum and hypothalamus incorporated amino acids more actively than those from cerebral cortex or hippocampus, when tested in a reticulocyte lysate system. Cerebellar mRNA also showed the highest activity for cDNA syntehsis as compared to mRNAs from the other three tissues.

Preparation of a cell-free extract from rat brain which can initiate protein synthesis in vitro

A cell-free protein synthesis system, derived from brains of 3 mo-old male Fischer-344 rats, has been characterized. The optimum conditions for amino acid incorporation in the system were 5 mM magnesium ion and 200 mM potassium ion. Incorporation depended on the addition of ATP, GTP, and an energy-generating system, and was sensitive to addition of the drugs aurintricarboxylic acid and sodium fluoride, inhibitors of initiation of protein synthesis. Both 40S and 80S initiation complexes were labeled in vitro, using [35S]methionine. Such labeling was sensitive to the protein synthesis inhibitors, aurintricarboxylic acid and sodium fluoride. The system, which can initiate protein synthesis, should be of use for examining mechanisms which underlie alterations in rat brain protein synthesis induced by various treatments.

Structure and biological activity of polysomes stained with Coomassie blue

Polysomes prestained with Coomassie blue were fractionated on sucrose density gradients giving rise to visible bands corresponding to different size classes of aggregates. Coomassie blue staining enhanced the capacities of brain and liver polysomes to synthesize proteins in vitro, including the synthesis of neuron-specific enolase. This positive action of the dye was restricted to polysomes and was not manifested when mRNAs isolated from prestained polysomes were tested in in vitro translation or reverse transcription, indicating that the action of the dye consists in stabilization of polysomal structure.

Effects of trichothecenes (T-2 toxin) on protein synthesis in vitro by brain polysomes and messenger RNA

The effects of T-2 toxin on protein synthesis were tested in two reticulocyte lysate in vitro systems pretreated with micrococcal nuclease. One of the test systems contained purified globin mRNA and was initiation dependent. The other contained rat brain polysomes and incorporated amino acids by an elongation dependent process. T-2 toxin inhibited the translation of globin mRNA at all concentrations tested, from 10(-8) M to 10(-4) M. Rat brain polysomes were much less sensitive to T-2 toxin than globin mRNA. While high concentrations of the toxin (10(-4) M) led to partial inhibition of protein synthesis by polysomes, low concentrations (10(-8) M and 10(-6) M) stimulated protein synthesis. Comparison of the above results with those obtained by other workers suggest that the T-2 toxin may inhibit not only the initiation step of translation, but also elongation and termination, depending upon the concentration of the toxin and the nature of the translation system. A similar mechanism may operate for all the trichothecene toxins that exert their effect through binding to ribosomal peptidyl transferase.