Chung H K, Kordyban S, Cameron L, Dobos P
Department of Microbiology, College of Biological Sciences, University of Guelph, Ontario, Canada.
Virology. 1996 Nov 15;225(2):359-68. doi: 10.1006/viro.1996.0610.
Drosophila X virus represents the entomobirnavirus genus of the Family Birnaviridae. Segment A of this bisegmented dsRNA containing virus was cloned and sequenced. The 3360-bp-long nucleotide sequence revealed the presence of two open reading frames (ORFs). A large ORF of 3096 nucleotides, which is flanked by a 107-bp 5' and a 157-bp 3'-untranslated region, and a 711-nucleotide-long small ORF located within the carboxy half of the large ORF but in a different reading frame. The large ORF encodes a 114-kDa polyprotein which is cotranslationally processed by the virus-coded protease VP4 to generate preVP2, VP3, and VP4 (VP1 is encoded by genome segment B). N-terminal amino acid sequencing of VP3 and VP4 established the order NH2-preVP2-VP4-VP3-COOH within the polyprotein. The small ORF straddles the VP4/VP3 junction and is capable of encoding a basic, arginine-rich 27-kDa polypeptide which so far has not been detected in infected cells. The amino acid sequences specified by the two ORFs were compared to those of infectious pancreatic necrosis virus (IPNV) and infectious bursal disease virus (IBDV) that represent the two other genera (aquabirnavirus and avibirnavirus) of the Birnaviridae family. Significant sequence homology among the three viruses was found to be restricted to the amino and carboxy regions of preVP2 and to a small 21-residue-long domain near the carboxy terminal region of VP3. Significant sequence homology is exhibited by the small ORFs of the three viruses.
果蝇X病毒属于双RNA病毒科的昆虫双RNA病毒属。对这种含双链RNA的双节段病毒的A节段进行了克隆和测序。3360个碱基对长的核苷酸序列显示存在两个开放阅读框（ORF）。一个3096个核苷酸的大ORF，其两侧分别是107个碱基对的5'非翻译区和157个碱基对的3'非翻译区，以及一个711个核苷酸长的小ORF，位于大ORF的羧基端一半内，但阅读框不同。大ORF编码一个114 kDa的多蛋白，该多蛋白由病毒编码的蛋白酶VP4进行共翻译加工，产生前VP2、VP3和VP4（VP1由基因组B节段编码）。VP3和VP4的N端氨基酸测序确定了多蛋白内的顺序为NH2-前VP2-VP4-VP3-COOH。小ORF跨越VP4/VP3连接点，能够编码一种富含精氨酸的碱性27 kDa多肽，目前在感染细胞中尚未检测到该多肽。将这两个ORF指定的氨基酸序列与代表双RNA病毒科另外两个属（水生双RNA病毒属和禽双RNA病毒属）的传染性胰腺坏死病毒（IPNV）和传染性法氏囊病病毒（IBDV）的氨基酸序列进行了比较。发现这三种病毒之间的显著序列同源性仅限于前VP2的氨基和羧基区域以及VP3羧基末端区域附近一个21个残基长的小结构域。这三种病毒的小ORF表现出显著的序列同源性。
