(A) Physical characterization of YACs in yeast. Chromosome-size DNA was isolated from yeast transformants, exposed to a low dose of gamma rays, separated by CHEF gel electrophoresis, and blot-hybridized with a Sat probe. Lanes 1–12 correspond to 12 independent yeast isolates. The size of inserts varied from 50 to 400 kb. Lanes 2, 3, 4, 5, 7, 8, 10, 11 and 12 on the gel correspond to YACs 8, 11, 13, 16, 25, 26, 41, 59 and 2 in Table 1. Lanes 1, 6 and 9 correspond to additional independent YAC isolates. (B) YAC DNAs were digested with HindIII, EcoRI or XbaI, gel-separated, and blot-hybridized with either a Sat or Alu probe.