FIG. 2.

Characterization of mutants with nucleotide substitutions in the C-rich region of the spacer. Nucleotide sequences (nt 87 to 103) of the C-rich region in mutants used in these studies are shown. Dashes represent the nucleotides conserved between WT [PV1(M)] and the mutants. Boxed sequences indicate the C-rich regions in the spacer. RNA transcripts of the WT and mutant viruses were transfected into HeLa cells, and the time of CPE was determined (see Materials and Methods). Viruses that gave no CPE after transfection were passaged one or more times. RNAs derived from viruses that emerged after transfection were reverse transcribed, and their DNA sequences were determined. The arrow indicates the location of a C residue insertion in revertant MR9. Dots indicate deletions of nucleotides in the revertants. n.r., no revertant was obtained.