- 期刊
Comparison of the Genetic organization of Papaya Ringspot Virus with Other Potyviruses
木瓜輪點病毒基因組成和其他馬鈴薯Y群病毒之比較
摘要
木瓜輪點病毒(PRSV)的基因體RNA的全長度核酸序列，業已解出，病毒基因體共含10326個核苷酸(不含3'poly A尾端)，和已解出序列的馬鈴薯Y病毒(potyviruses)中的菸草蝕刻病毒(TEV,9496核苷酸)、菸草脈斑病毒(TVMV,9472)、李子疹斑病毒(PPV,9741)、馬鈴薯Y病毒(PVY,9740)、碗豆種傳病毒(PSbMV,9924)、大豆嵌紋病毒(SMV,9588)及番椒斑紋病毒(PeMV,9640)相較爲最長者。PRSV RNA的鹽基組成爲A 31.2%、U 27.0%、G 23.0%, C 18.0%,和其他potyviruses相似。其基因體RNA只含一大轉譯架構，由86至88核苷酸處起始轉譯至第10118止，對映出一含3344個胺基酸的複合蛋白，此複合蛋白比其他potyviruses大138-139個胺基酸。PRSV RNA 3'端非轉譯區含85核苷酸，比其他potyviruses相較顯示，在75%類似度時5'端具有一個共同序列NAAAUAAAACANNUCAANACAACAUAA，此5'端共同區可能和potyviruses病毒複製共通主要功能有關。PRSV的基因組成和其potyviruses類似，但複合蛋白N端所産生的第一個蛋白(PI)爲63K,比其他potyviruses大了18-34 K。P1蛋白係所有potyvirus蛋白中期歧異度最大者，可視爲區別不同potyviruses之主要性狀。在所有蛋白中，以NIb蛋白共同性最高，此蛋白被認爲是RNA的複製酶。PRSV蛋白裂解過程由病毒產生的三種裂解酵素執行，其中P1蛋白酶及HC-Pro蛋白酶分別自行切解C端，而NIa蛋白酶以順反方式切解複合蛋白產生CI、P5、NIa、NIb、及CP等蛋白。所有potyviruses經比較顯示，Nla蛋白中有一內含切位可分解其為VPg及蛋白酶二蛋白。在有些potyviruses上，CI蛋白上游上有一可能被NIa蛋白酶認識之切位，可產生─6 K之蛋白。Potyviruses的基因體RNA經比較之後可以歸納爲VPg-5'端引導序列-P1蛋白-HC Pro蛋白-P3蛋白-CI蛋白P5蛋白-Nla VPg蛋白-Nia Pro蛋白-NIb蛋白-鞘蛋白-3'端非轉譯區-Poly A尾端。
並列摘要
The complete nucleotide sequence of papaya ringspot virus (PRSV) RNA has recently been determined by our laboratory. The PRSV genome contains 10326 nucleotides excluding the 3' terminal poly (A) tail. PRSV RNA is larger than those of seven sequenced potyviruses: tobacco etch virus (TEV) RNA is 9496 nucleotides, tobacco vein mottling virus (TVMV) RNA 9472, plum pox virus (PPV) RNA 9741, potato virus Y (PVY) RNA 9704, pea seed-borne mosaic virus (PSbMV) RNA 9924, soybean mosaic virus (SMC) RNA 9588, and pepper mottle virus (PeMV) RNA 9640. The base composition of PRSV RNA shows a high adenine content(31.2%), followed by uraci (27.0%), guanine (23.8%), and cytosine (18.0%), similar to those of the other potyviruses The genomic RNA of PRSV contains one large open reading frame that starts at nucleotide positions 86 to 88 and ends at position 10118, encoding a polyprotein of 3344 amino acids which 138-339 residues longer than those of the other The 5' leader sequence contains 85 nucleotides,46 to 121 nucleotides shorter than those of the other potyviruses. The 3' non-coding region contains 209 nucleotides, which is in common with the other potyviruses (163-331, average 240 nucleotides). The conserved sequence of NAAAUAAAACANNUCAANACAACAUAA at the 5' end of PRSV and those of seven other potyviruses shows 75% similarity, suggesting that region may play a common important role for potyvirus replication. The genetic organization of PRSV is similar to that of other potyviruses except that the first protein (P1) processed from the N terminus of the polyprotein has an M_r of 63 K, 18-34 K larger than those of the other potyviruses. The P1 protein is the most variable protein among potyviruses and may be considered important for identification of individual potyvirus. The most conserved protein of potyviruses appears to be the NIb protein, the putative polymerase for the replication of potyviral RNA. The protein processing of potyviruses is mediated by three virus-encoded proteinases: the P1 protein liberates its own C terminus, the HC-Pro proteinase also autocatalytically cleaves its C terminus, and the Nla protein which is responsible for cis and trans proteolytic processing to generate the CI, P5, Nla, NIb, and coat proteins. An internal cleavage site for delimitation of the genome-linked protein (VPg) and proteinase domains in the NIa protein are present in all potyviruses compared. A suboptimal cleavage site upstream the Cl protein, recognized by the NIA proteinase and potentially generates a protein of 6 K, is present in several potyviruses. The genetic organization of potyviruses is summarized as VPg-5' end leader-P1 protein-HC Pro protein-P3 protein-Cl protein-P5 protein-Nia VPg protein-NIa Pro protein-NIb protein-coat protein-3' non-coding region-poly (A) tract.