GENOME PROPERTIES OF BEET VIRUS-Q, A NEW FURO-LIKE VIRUS FROM SUGAR-BEET, DETERMINED FROM UNPURIFIED VIRUS

Based solely on the information that beet virus Q (BVQ) contains tubul ar particles, the entire nucleotide sequence of its tripartite genome was determined from unpurified virus in ca, 40 ml crude sap from local ly infected Chenopodium quinoa, A starting sequence for RNA 1 was gene rated using primers corresponding to highly conserved helicase domains in the respective RNAs of furo-, pomo-, peclu-, hordei- and tobraviru ses, and was extended by a walking random-primed cDNA approach. The si milarity of the 3' ends of furoviral RNAs allowed starting sequences f or BVQ RNAs 2 and 3 to be obtained once the 3' end of RNA 1 was known. BVQ RNA 1 encodes a protein with a methyltransferase-like, a variable and a helicase-like region, and for a readthrough protein which, in a ddition, contains an RNA-dependent RNA polymerase region. RNA 2 carrie s the coat protein gene, a coat protein readthrough protein gene and t wo additional ORFs which may have arisen by deletions from an original ly larger readthrough domain. RNA 3 carries a triple gene block resemb ling that of several other rod-shaped viruses. The 5' UTRs of the thre e RNAs have the potential to form a series of hairpins with C-A and C- C mismatches resembling those found in tymoviral RNAs, The 3' ends can be folded into tRNA-like structures which are preceded by a long hair pin-like structure and an upstream pseudoknot domain. BVQ belongs to t he recently proposed genus Pomovirus; it shows evolutionary relationsh ips to furoviruses in sensu stricto, peclu-, hordei-, tobra-, tymo-, t obamo-, carla- and potexviruses.