Three highly purified preparations (preparations I, II-1, and 11-2) have been obtained from wheat germ and shown to support in vitro polypeptide synthesis directed by capped or uncapped mRNAs in a eukaryotic initiation factor 4B (eIF-4B)-deficient system. The three preparations differ, however, in polypeptide composition and in the ability to overcome the inhibitory effect of 7-methylguanosine 5'-triphosphate (m7GTP) on in vitro polypeptide synthesis. Preparation I contains two polypeptides (Mr = 80,000 and 28,000), which are present in a 1:1 molar ratio and are associated in a high molecular weight complex. Preparation II-1 contains two major polypeptides (Mr = 220,000 and 26,000) and preparation II-2 also contains two major polypeptides (Mr = 110,000 and 26,000). Preparations II-1 and 11-2 are high molecular weight complexes; neither contains detectable amounts of a Mr 80,000 or a Mr 50,000 component. Preparations 11-1 and II-2 both overcome m7GTP inhibition, whereas preparation I does not. These findings raise several questions with regard to the identity of eIF-4B and its relationship to cap recognition factors.
The 3′‐terminal tRNA‐like structure in turnip yellow mosaic virus (TYMV) RNA can be adenylated by tRNA nucleotidyltransferase and subsequently aminoacylated by valyl‐tRNA synthetase.Here we present evidence that TYMV Val‐RNA can form a stable complex with eukaryotic wheat germ elongation factor EF‐1alpha and GTP: the Val‐RNA is protected by EF‐1alpha.. GTP against digestion by RNase A. By affinity chromatography of TYMV Val‐RNA fragments on immobilized EF‐1alpha . GTP, it has been established that the valylated aminoacyl RNA domain, which in TYMV RNA is formed by the 3′ half of the tRNA‐like region, is sufficient for complex formation with EF‐1alpha . GTP. The aminoacyl RNA domain is equivalent in tRNAs to the continuous helix formed by the acceptor stem and the T stem and loop. In line with these results, the aminoacyl RNA domain in TYMV Val‐RNA complexed to EF‐1 alpha . GTP is resistant to digestion by RNase A. It is also shown that the TYMV RNA replicase (RNA‐dependent RNA polymerase) isolated from TYMV‐infected Chinese cabbage leaves does not contain tRNA nucleotidyltransferase, valyl‐tRNA synthetase or EF‐1alpha. This suggests that interaction of TYMV RNA with EF‐1alpha is not mandatory for replicase activity.
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