Functional characterization of the genomic promoter of borna disease virus (BDV): implications of 3'-terminal sequence heterogeneity for BDV persistence.

Borna disease virus (BDV) is an enveloped virus with a genome organization characteristic of Mononegavirales. However, based on its unique features, BDV is considered the prototypic member of a new virus family, Bornaviridae, within the order Mononegavirales. We have described the establishment of a reverse genetics system for the rescue of BDV RNA analogues, or minigenomes, that is based on the use of polymerase I/polymerase II. Using this BDV minigenome rescue system, we have examined the functional implications of the reported sequence heterogeneity found at the 5' and 3' termini of the BDV genome and also defined the minimal BDV genomic promoter within the 3'-terminal 25 nucleotides. Our results suggest that the accumulation of RNA genome species containing truncations of one to three nucleotides at their 3' termini may contribute to modulate BDV RNA replication and gene expression during long-term persistence.