PMB Lab., International Center for Genetic Engineering and Biotechnology, New Delhi-110067.
Abstracts of Research Papers Presented during the National Symposium of Indian Virological Society at Unit of Plant Virology, Division of Plant Pathology, Indian Agricultural Research Institute, New Delhi-110 012, October 14–1.
Indian mungbean Yellow mosaic virus (IMYMV), a member of begomovirus genus of the family Geminiviridae and the most potent phytopathogen of legume cultivation, serves as an important model system to study the mechanism of Gemini viral DNA replication. The DNA-A component the bipartite genome of any begomovirus is necessary for the viral DNA replication. The virus encoded Rep protein (or AC1) cleaves the viral strand of the replicative form at a particular site of the replication origin to start the rolling circle replication (RCR). Here we report for the first time that Rep also forms part of the ongoing RCR-fork as a helicase protein. Evidences will be provided to claim that the other viral factors, namely AC3 and AC5, might act as accessory factors for the Rep-mediated helicase activity.
Besides the activities mentioned above, probably more than a dozen of host-encoded factors would be required for the viral RCR. Some of these factors have been found in the case of other begomoviruses, namely TGMV and BGMV etc. We have shown that the host PCNA protein interacts with IMYMV-Rep and might help control the viral DNA copy number in the infected plant. The single-stranded DNA binding protein RP A also plays a role in IMYMV-RCR since a component of RP A, namely the 32kDa protein, interacts with Rep via its Walker-A domain. The Rep-32kDa protein-protein interaction also leads to enhanced ATPase and helicase activities of Rep, suggesting that RP A could be part of the RCR-fork along with the Rep protein. We have developed a yeast model for IMYMV replication to probe the various host factors participating in viral DNA replication. The host factors identified so far, using the yeast model, will be discussed.
