Characterization of retroviral insertion. (A) Top shows structure of an integrated provirus containing a cDNA fragment in LNCX vector. LTR, long terminal repeat; neo, neomycin-resistant gene; CMV, cytomegalo viral promoter. Restriction enzymes that cut once in the genome are indicated. Bottom shows sequence comparison of cDNA fragment to mouse 18S rRNA gene. (B) Southern blot analysis. DNA was prepared from CCE ES cells (lanes 1) and EB-PE cells (lanes 2) and digested with BamHI, HindIII and BglII,BamHI and BglII, or Sph I. Digested DNA was run on an agarose gel and transferred to a nylon membrane and probed with either CMV promoter or neo.