Date of Award


Degree Type


Degree Name

Doctor of Philosophy


We have used in vitro translation to analyze the protein products produced from the genomic RNAs of members of the potexvirus group, namely, papaya mosaic virus (PMV), clover yellow mosaic virus (CYMV), viola mottle virus (VMV), barrel cactus virus (BCV), and foxtail mosaic virus (FTMV). Polyacrylamide gel electrophoresis of polypeptides made in vitro from the genomic RNAs of these viruses indicated that only PMV and CYMV RNA directed the synthesis of polypeptides which have the same molecular weight and antigenic determinants as their respective coat proteins. All viral RNAs tested in vitro produced high molecular weight polypeptides. Peptide mapping of these high molecular weight polypeptides for PMV and CYMV has indicated that they are related to each other but not to their respective coat proteins. The ability of partially encapsidated PMV and CYMV ribonucleoprotein particles to direct protein synthesis has also been assessed. As the extent of encapsidation increased, the relative synthesis of the high molecular weight products decreased markedly. In contrast, the synthesis of the in vitro coat protein not only persisted but increased relative to the untreated RNA until a substantial fraction of the RNA is encapsidated. In view of the polarity of assembly in vitro this finding indicated that the cistron for PMV and CYMV coat protein is localized towards the 3' end of the RNA. We have also examined the relationship of these viral genomes at the level of nucleotide sequence. Using RNA-cDNA hybridization we found that no homology exists between all members of the potexvirus group tested, not with unrelated members. As a further means of characterizing the genomes of these viruses, we have constructed double-stranded cDNA copies of PMV and CYMV RNA and have subsequently cloned them in E. coli using the plasmid pBR322 as a vector.



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