Prediction of functional regions of the maize streak virus replication-associated proteins by protein-protein interaction analysis

The replication of the,geminiviruses depends on the viral encoded early (co mplementary-sense) proteins and on host genome encoded factors. Additionall y, some of the early proteins (the AL2 protein of subgroup III, and the Rep A (formerly known as C1) or Rep (C1:C2) proteins of subgroup I geminiviruse s) can function as transcriptional activators of virion- (V-)sense gene exp ression. The yeast two-hybrid system has allowed us to predict some of the functionally important regions of the maize streak virus (MSV) early protei ns RepA and Rep. Defined domains of these proteins were shown to act as tra nsactivators in yeast cells. We detected the association of the RepA and Re p proteins, and their subfragments, with the maize retinoblastoma protein ( ZmRb1) which is likely to be one of the interacting host proteins. We showe d the self-association capability of the MSV proteins and suggest that homo - or hetero-oligomerization may play an important role in virus replication . These results provide new insights into the role of different regions of the MSV proteins in relation to transcriptional activation and regulation o f viral DNA replication.