Polyamines, in particular spermidine and spermine, were shown to have a stimulatory effect on the incorporation of amino acids into protein in the wheat-germ cell-free system programmed with exogenous mRNA. The addition of the optimum concentrations of polyamines results in a lowering in the Mg2+ optimum for protein synthesis. At the optimum combination of spermidine and Mg2+ the rate of peptide chain elongation with tobacco mosaic virus RNA as messenger RNA was twice the rate observed at the optimum concentration of Mg2+ in the absence of polyamines, but there was no significant difference in the rate of chain initiation under these two conditions. The presence of polyamines also increased the yield of full-length translation products from the viral RNA with a corresponding reduction in the short polypeptide products. These short products are shown to be incomplete translation products that accumulate mainly in the form of peptidyl-tRNA associated with 80-S ribosomes which can release the incomplete nascent chains on incubation with puromycin. The origin of these incomplete chains may be due to endonucleolytic cleavage of mRNA, which we have demonstrated occurs at a significant rate in our system. It is proposed that the increased rate of elongation in the presence of polyamines raises the probability of ribosomes completing the synthesis of full-length products before the mRNA is degraded.Polyamines are organic polyvalent cations found in abundance in both prokaryotic and eukaryotic cells, the total concentrations of polyamines being nearly equal to that of intracellular Mg2+ [l]. Many workers have shown that polyamines can play an important role in vitro in a number of macromolecular biosynthetic processes involving nucleic acids [ 11, such as DNA-primed RNA transcription [2]. The importance of polyamines in vivo is shown by the fact that mutants of Escherichia coli unable to synthesize polyamines require exogenous polyamines for growth [3].There have been many reports that polyamines can enhance protein synthesis both in prokaryotic and eukaryotic cell-free systems although in no case can they completely replace the Mg2 synthesis in a gel-filtered rabbit reticulocyte lysate could only be restored to the level seen in the untreated lysate by readdition of the polyamines which had been removed by gel filtration [5]. Since the rate of protein synthesis in the untreated lysate is very near the rate found in intact cells, we concluded that polyamines are obligatorily required for maximum rates of protein synthesis, and that polyamines and M$+ are the only polyvalent cations needed. Since the wheat-germ cell-free system as used in most laboratories is prepared by gel-filtration of a wheatgerm extract, and would therefore be expected to be deficient in polyamines, we have investigated the effects of polyamines on protein synthesis in this system. We show here that polyamines not only enhance the rate and extent of protein synthesis but also lead to the synthesis of full-length products in higher yield with a corres...

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The pathogenesis of H. contortus infection in lambs under 6 months of age challenged orally with 10,000 third stage infective larvae is described. The development of the parasite and its relationship to haematological and pathological changes are discussed, with particular reference to specific cellular mobilizations, and detailed descriptions are given of the haematology and parasitology, gross pathology and histopathology at 4, 7, 12, 18, 22 and 35 days after infection. Dramatic changes had developed by day 12.