PARTIAL CHARACTERIZATION OF THE LETTUCE INFECTIOUS YELLOWS VIRUS GENOMIC RNAS, IDENTIFICATION OF THE COAT PROTEIN GENE AND COMPARISON OF ITS AMINO-ACID-SEQUENCE WITH THOSE OF OTHER FILAMENTOUS RNA PLANT-VIRUSES

Purified virions of lettuce infectious yellows virus (LIYV), a tentati ve member of the closterovirus group, contained two RNAs of approximat ely 8500 and 7300 nucleotides (RNAs 1 and 2 respectively) and a single coat protein species with M(r) of approximately 28000. LIYV-infected plants contained multiple dsRNAs. The two largest were the correct siz e for the replicative forms of LIYV virion RNAs 1 and 2. To assess the relationships between LIYV RNAs 1 and 2, cDNAs corresponding to the v irion RNAs were cloned. Northern blot hybridization analysis showed no detectable sequence homology between these RNAs. A partial amino acid sequence obtained from purified LIYV coat protein was found to align in the most upstream of four complete open reading frames (ORFs) ident ified in a LIYV RNA 2 cDNA clone. The identity of this ORF was confirm ed as the LIYV coat protein gene by immunological analysis of the gene product expressed in vitro and in Escherichia coli. Computer analysis of the LIYV coat protein amino acid sequence indicated that it belong s to a large family of proteins forming filamentous capsids of RNA pla nt viruses. The LIYV coat protein appears to be most closely related t o the coat proteins of two closteroviruses, beet yellows virus and cit rus tristeza virus.