Southern blot analysis of viral DNA. Luminogram of electrophoretically separated, Nco I-digested and hybridized viral DNA fragments. Viral DNAs were prepared from large scale cultures of Vero cells infected with the recombinant viruses, digested with Nco I, electrophoretically separated on an agarose gel, transferred to a Zeta probe membrane, and hybridized with digoxigenin-labeled 1.8 kb Nco I fragment of the Bam HI S. The predicted sizes of the bands generated by the digestions shown in Fig. 1 are approximately 1.8 kb for band A, 0.7 kb for band B, and 2.2 kb for band C. The 80 bp band (Fig.1, line 6) was too small to be detected in this electrophoresis. Viral DNA from two different plaques of R5225 were analyzed (the two lanes labeled as R5225).