Isolation of episomal bovine papillomavirus chromatin and identification of a DNase I-hypersensitive region.

The investigation of papillomavirus chromatin has been hampered by the unavailability of a tissue culture system for vegetative growth of these viruses. We have used, therefore, bovine papillomavirus type 1-transformed hamster embryo fibroblasts containing 200 to 250 episomal genome equivalents per cell as a source of viral chromatin. The selectively isolated chromatin was shown to be slightly larger (80S) than the mature simian virus 40 chromatin, which was cosedimented in a sucrose density gradient. Both Fo I and Fo II were present in the bovine papillomavirus type 1 chromatin. A fast-sedimenting fraction, whose structure is still unknown, also contained oligomeric bovine papillomavirus type 1 DNA. By in situ DNase digestion of isolated nuclei and subsequent cleavage of the bovine papillomavirus type 1 DNA with various restriction endonucleases, a major DNase-hypersensitive region was detected in the chromatin. This region, comprising approximately 320 base pairs, is located between the relative physical map positions 0.88 and 0.92.