PFGE analysis of Asc I and AscI/Mlu I fragments from BJ DNA. The Asc I fragments (700 and 560 kb) are common for the three probes showing the existence of a PAR cluster. The double digest gave a partial 700-kb Asc I fragment, the smaller 560-kb fragment was not detected. Asc I shows marked site preference, and we obtained variable amounts of cleavage at this site in different digests. The AscI/Mlu I digest shows that PAR-3 is located at one end of the PAR cluster. PAR-1 and PAR-2 are located on a 390-kb fragment while PAR-3 is seen on a separate 310-kb fragment (and on a shorter 140-kb fragment). PFGE conditions: ramp from 110 to 140 seconds for 64 hours.