Deciphering the mechanism of defective interfering RNA (DI RNA) biogenesis reveals that a viral protein and the DI RNA act antagonistically in virus infection.

Potato mop-top virus (PMTV) produces a defective RNA (D RNA) encompassing the 5'-terminal 479 nucleotides (nt) and 3'-terminal 372 nt of RNA-TGB (where TGB is triple gene block). The mechanism that controls D RNA biogenesis and the role of D RNA in virus accumulation was investigated by introducing deletions, insertions, and point mutations into the sequences of the open reading frames (ORFs) of TGB1 and the 8-kilodalton (8K) protein that were identified as required for efficient production of the D RNA. Transient expression of RNA-TGB in the absence of RNA-Rep (which encodes the replicase) did not result in accumulation of D RNA, indicating that its production is dependent on PMTV replication.