Enhanced nicking activity of Rep in presence of pre-coat protein of Mungbean yellow mosaic India virus

Abstract

Yellow mosaic disease causes severe yield loss in grain legumes in Indian subcontinent and south east Asia. The disease is caused by two virus species, Mungbean yellow mosaic India virus (MYMIV) and Mungbean yellow mosaic virus (MYMV). They have genome organization typical of Old World begomoviruses, the unique feature being the presence of an open reading frame (ORF) AV2 upstream of coat protein gene. In order to elucidate its function, ORF AV2 of blackgram isolate, Mungbean yellow mosaic India virus-[India:New Delhi:Blackgram 3:1991] MYMIV-[IN:ND:Bg3:91] and cowpea isolate, Mungbean yellow mosaic India virus-[India:New Delhi:Cowpea7:1998] MYMIV-[IN:ND:Cp7:98], respectively, were over expressed in Escherichia coli in fusion with maltose binding protein (MBP). The recombinant protein did not show efficient binding to DNA. However, both MBP-BgAV2 and MBP-CpAV2 proteins modulated nicking and ATPase activity of replication initiation protein (Rep). Even low concentration, 20 ng of MBP-BgAV2 and MBP-CpAV2 could bring 20 folds increase in nicking activity of Rep. Similarly in the presence of AV2 protein, two to three fold increase in ATPase activity was observed. It is hypothesized that AV2 protein may play a role of accessory protein modulating Rep activities.