Subculture requirement for rescue of SV40 from 'nonrescuable' cell lines.

Virus could be rescued by cell fusion techniques from the H50, BRKSV (Bam I linear), 14B and 14B (1--4) cell lines, which contain the entire SV40 genome but have previously yielded negative results by this method. Virus could not be rescued from the T22 cell line, which was transformed by defective virus. The T-antigen-negative flat revertant cell line, 14B (1--4), converted to T-antigen-positive prior to rescue. Subculture and extensive monitoring for production of infectious virus appeared to be prerequisite for detecting virus rescue.