摘要：

wheat germ extract programmed with reovirus mRNA. In allsubsequent experiments edeine was used at a concentrationbetween 3 and 4 pM. It has been previously reported thatedeine is a specific inhibitor of polypeptide initiation in retic-ulocyte lysates (2) and we confirmed, in the wheat germsystem, absence of an effect on elongation. This is shown inFig. IB, in which translation was permitted to occur for 4 min,at which time the cap analogue pm7G was added, to inhibitfurther initiation events (17). This resulted in continued aminoacid incorporation up to about 20 min, when a plateau oc-curred. Amino acid incorporation during the 4- to 20-mininterval in the presence of pm7G (at a rate of about 20 to 40amino acids/min) is considered to represent polypeptide elon-gation exclusively, and failure of edeine to reduce this incor-poration, as shown in Fig. lB, indicates that the inhibitoryeffect of edeine is limited to initiation. In contrast with pmiGand edeine, sparsomycin added at 4 min caused immediateand complete cessation of amino acid incorporation, confii-ing that the kinetic assay can distinguish between inhibitorsof initiation and inhibitors of elongation. Although previous reports have described accumulation of40 S (or 50 S), and some 70 S complexes in edeine-treatedlysates, we found that the size of the edeine-induced com-plexes varied, predictably, with the size of the mRNA. Withsmall RNA species, such as a 44-nucleotide fragment derivedfrom the 5' terminus of one of the reovirus messages, glycerolgradient analysis showed that edeine abolished 80 S initiationcomplex formation and caused the labeled mRNA fragmentto accumulate in 40 S complexes (Fig. 2A). When full lengthreovirus mRNA molecules were used, however, edeine causedformation of rapidly sedimenting complexes. For example

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