Common features of polyomavirus mutants selected on PCC4 embryonal carcinoma cells

The genomic rearrangements of six polyomavirus mutants selected on PCC4 embryonal carcinoma cells have been compared and their common characteristics pointed out. All mutants show a duplication which includes at least the adenovirus type 5 (Ad5) E1A‐like enhancer core sequence plus a deletion of variable size and location. The presence of the second enhancer core sequence, the SV40‐like enhancer, is not required for expression of the PyEC PCC4 phenotype. Two of these mutants are also able to express polyomavirus T antigen on F9 and LT1 cells. Multiadaptation seems to require the duplication of the Ad5 E1A‐like core sequence, the maintenance of the SV40‐like core sequence and a local change in DNA stability.