



Vector–hexamer PCR products. (a) Products of the initial PCR using the outermost YAC vector right arm primer R-I with thePvuII primer. Only nonspecific products are visible. (b) Products of the second round of PCR using the first nested right arm primer R-II with the PvuII primer. Both nonspecific and a few specific products are visible. (c) Products of the third round using the second nested right arm primer R-III with thePvuII primer. Bright YAC-specific products are apparent in many lanes. (d) Third-round PCR products from several different YACs made with the left arm L-III primer in conjunction with three different hexamer primers. The center gel demonstrates a background band amplified from the yeast host near the position of the largest size marker band (φX174 digested with HincII) in all four YACs and the control YAC.











