FIG. 1.

Recombinant CDVs. (A) CDV genome and mutations introduced. The genome is shown as a white elongated box. The genes are indicated with the letters N (nucleocapsid), P (phosphoprotein), M (matrix), F (fusion), H (hemagglutinin), and L (large or polymerase). Above the genome, a segment of the H protein amino acid sequence is shown, and the six residues mutated to alanine or serine (A or S, one-letter amino acid code) are indicated. These mutations make this virus selectively receptor blind (SLAMblind). Below the genome, a schematic drawing illustrates the three proteins (V, P, and C from the top) generated by the P gene. The three mutations selectively ablating C protein expression (elimination of the start codon by mutation to ACG and introduction of two stop codons, UGA and UGA) are indicated in red above the P gene nucleotide sequence (nucleotides 20 to 60 covering the beginning of the C reading frame, Cko). The five mutations selectively ablating V protein expression (four mutations in the editing sequence, C, G, A, A, and introduction of a stop codon, UGA) are indicated in red above the P gene sequence (nucleotides 670 to 710, Vko). The VCko virus has all eight mutations (not shown). (B) Immunoblot analysis of the P gene products expressed by the wild-type virus 5804P and its three derivatives, Cko, Vko, and VCko. Antisera against the common amino-terminal end of the P and V proteins (upper panel) or against the C protein (lower panel) were used. ctr, uninfected cell control. (C and D) Growth curves of the four viruses on VerodogSLAMtag cells. The multiplicity of infection was 0.01. The titers of virus released in the supernatant are shown in panel D; those of cell-associated virus are shown in panel C. TCID₅₀, tissue culture 50% infective dose.