Southern and Northern analysis of expressed X-linked sequences and cDNA clones. (A) A 2.2-kb genomic fragment, FIJG, was hybridized to a Southern blot containing DNA digested with HindIII and either XbaI or BglII. The lanes correspond to female genomic DNA (GM7341), and two somatic cell hybrids retaining reciprocal portions of a t(X;17) (6). A62–1A-4b contains Xp11.21-qter, and L62–3A contains Xp11.21-pter (37). This probe detects two loci in genomic DNA, one of which maps distal to the t(X;17) breakpoint (5.5- and 3.3-kb bands, referred to as FIJG-4), whereas the other maps proximal to the breakpoint (8.0-kb band, referred to as FIJG-5). The probe is colinear with genomic DNA and does not contain HindIII, XbaI, or BglII restriction sites. (B) Expression patterns were examined on a multiple-tissue Northern blot (CLONTECH) by using the same 2.2-kb genomic probe. A transcript of ≈1.3 kb was detected in skeletal muscle tissue only. (C) Secondary selected cDNA products from a typical direct cDNA selection experiment were used as a complex probe and hybridized to EcoRI digests of a partial cosmid contig covering the region that was selected (lanes 1–17). Hybridizing fragments correspond to genomic fragments homologous to selected cDNA clones. (D) The selected cDNA clone ADS9 is widely expressed and detects on Northern blots a single RNA species of ≈1.0 kb in various tissues.