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甜菜黑色焦枯病毒卫星RNA序列、结构与功能研究

郭立华

  Full-length sequence of a satellite RNA (sat-RNA) comprised of 615 nucleotides was determined from Beet black scorch virus isolate XJ (BBSV-XJ), which shared no extensive sequence homologies with its helper and any other virus reported. Multimeric sat-RNA molecules were identified in total RNA or purified virus particles, including single-stranded plus sense monomer, dimer and tetramer, or double-stranded monomer and dimer. By coinoculation of Chenopodium amaranticolor with in vitro transcripts of sat-RNA, along with BBSV genome RNA, the monomer, dimer or tetramer was reproduced not only autogenously, but also heterogeneously for each other, except the synthesized trimer was replicated only heterogeneously for the monomers, dimers and tetramers. Although deletions (58 to 133 bases) were found variably in the 3 -terminal sequence joined to the intact 5end of the next monomeric unit of multi-meric sat-RNAs, dimeric sat-RNA was preferentially accumulated when it had deletions (5 or 10 bases) or insertion (15 bases) within the junction regions, while replication of synthesized monomeric sat-RNA was seriously inhibited by deletion of 5 nucleotides in either 3or 5proximal end. So, it was indicated that the sequences at 5or 3proximal end of monomer, or at the junction region of multimeric are very important for sat-RNA replication, in which the 3end might be recognized by the RNA replicase for efficient initiation and the 5end was responsible for termination of replication. By comparing the time-courses of replication initiated by in vitro synthesized monomer or multimers, dimeric form was presumed as an intermediate for replication of sat-RNA. Besides of the mechanism that multimeric sat-RNA was resulted from linear monomer by template-switching of RNA polymerase between terminal sequences proposed previously, we proposed that the replicative process can be inverted from multimer, perhaps mainly as dimer, to monomer by mature termination of RNA replicase on 5end of junction, otherwise sat-RNA retains multimeric form duo to any modifying of junction region.……