A domain at the 3' end of the polymerase gene is essential for encapsidation of coronavirus defective interfering RNAs.

van der Most, R G; Bredenbeek, P J; Spaan, W J

Two murine hepatitis virus strain A59 defective interfering (DI) RNAs were generated by undiluted virus passages. The DI RNAs were encapsidated efficiently. The smallest DI particle, DI-a, contained a 5.5-kb RNA consisting of the following three noncontiguous regions from the MHV-A59 genome, which were joined in frame: the 5'-terminal 3.9 kb, a 798-nucleotide fragment from the 3' end of the polymerase gene, and the 3'-terminal 805 nucleotides. A full-length cDNA clone of the DI-a genome was constructed and cloned downstream of the bacteriophage T7 promoter. Transcripts derived from this clone, pMIDI, were used for transfection of MHV-A59-infected cells and found to be amplified and packaged. Deletion analysis of pMIDI allowed us to identify a 650-nucleotide region derived from the 3' end of the second open reading frame of the polymerase gene that was required for efficient encapsidation.