This figure shows the scheme for the construction of HAECs. The HAEC vector pH211 carries the EBV latent replication origin, oriP, which permits the propagation and stable episomal maintenance of 100-300 kb of HAECs in human cells. The HAEC vector is ligated to partially digested human genomic DNA of 100-400 kb. The unligated vector DNA and genomic DNA with sizes smaller than 100 kb are removed by a sucrose gradient. Ligated DNA is introduced into human cells by lipofection, which permits the transfer of large DNA. The cell transformants are selected by growing cells in the presence of hygromycin. The HAEC DNAs are easily isolated from mammalian cells and are ready for various molecular analysis (i.e. FISH, PCR, Southern Blot).