18 Quantitative DNA Fiber Mapping
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Preparation and purification of the circular DNA molecules is simple
and fast. An example of mapping an exon specific plasmid clone onto circular BAC molecules is depicted in Fig. 3C. The use of circular DNA molecules results in a dense deposition of circular DNA molecules in the presence of linear fragments of different sizes (Fig. 3B). The largest circles are
stretched to about -2.3 kb/l!m, but smaller, more condensed molecules
can also be analyzed using the extent of the vector-specific green -7
kb domain on BACs as standard for normalization. The linear fragments
Fig. 2. Quantitative DNA Fiber Mapping (QDFM) using phage DNA molecules. Lambda
DNA molecules immobilized on APS-derivatized glass slides were hybridized with a mixture
of biotin- and digoxigenin-Iabeled lambda DNA restriction fragments. The molecules show
specific labeling after incubation with avidin-FITC and rhodamine-labeled antibodies
against digoxigenin. The insert shows a typical molecule