FIG. 3.

Southern blot analysis for the involvement of L1 and AluSq elements in MVX-lacZneo integration. (A) The integration of MVX-lacZneo via homology-mediated recombination involving the L1 and/or the AluSq element flanking the neo^r cassette and their abundant cellular counterparts would lead to loss of the BgIII and/or BamHI site flanking these elements, resulting in BglII/BamHI fragments containing neo^r sequences with sizes different from the 3,492 bp generated from the complete vector. (B) Genomic DNA from U87MGneo^r clones 1 through 16 was digested with BglII and BamHI and hybridized with the 894-bp NcoI fragment (Fig. 1A) to detect neo^r sequences. As positive controls (PC), BglII/BamHI-digested pMVX-lacZneo corresponding to one and three copies/cell was used. DNA from original U87-MG cells was used as a negative control (NC).