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Conformational Changes Facilitate the in vitro Translation of Intact Virions of Robinia Mosaic Virus

Laboratory of Virology, Shanghai Institute of Biochemistry, Academia Sinica, Shanghai 200031, Peoples Republic of China

Intact virions of robinia mosaic virus (RoMV) which were inactive in a rabbit reticulocyte in vitro translation system when suspended in 10 mM-phosphate buffer pH 6.0, exhibited an efficient translation activity after treatment with 10 mM-phosphate buffer pH 8.0. The estimated M_r values of the translation products of the intact virions in vitro were 130K, 93K, 77K, 60K, 43K, 34K and 31K by SDS-PAGE. In comparison with the treated intact virions, the total viral genomic RNA produced only three polypeptides, of M_r approx. 31K, 25K and 22K. Circular dichroism (CD) measurements of the virions showed that the -helical structure of the viral coat protein subunits might undergo some conformational changes after treatment under mildly alkaline conditions. Fluorescence emission and quenching analysis indicated that the microenvironment of chromophores in the virions suspended in 10 mM-phosphate buffer pH 6.0 might be different from that of the virions in 10 mM-phosphate buffer pH 8.0. Both CD and fluorescence evidence suggested that as a result of conformational changes in the viral coat protein subunits, the fine structure of the virions might be altered after short exposure to the mildly alkaline buffer, although such alteration was undetectable by electron microscopy. The conformational changes of the viral coat protein subunits and consequently the alteration of the fine structure of the virions could facilitate the gene expression and uncoating of RoMV in vitro.

Keywords: RoMV, translation, uncoating

Received 23 January 1989; accepted 26 May 1989.