Restriction analysis of chromosomal sequences homologous to single-copy fragments cloned from small polydisperse circular DNA (spcDNA).

Restriction fragments from the fraction of small polydisperse circular DNA (spcDNA) were cloned in pBR322. The spcDNA was prepared from cell cultures derived from an angiofibroma of a patient with tuberous sclerosis (TS). Such cultures have been shown previously to contain increased amounts of spcDNA. Four cloned spcDNA fragments containing single-copy sequences were chosen to characterize the homologous chromosomal DNA segments by restriction analysis. When used as hybridization probes, these four fragments generate well-defined nonvariable patterns in the chromosomal DNA from healthy donors. The restriction patterns obtained with one of the fragments (D-C4) can best be interpreted by assuming the presence of two copies of the homologous sequences in chromosomal DNA. A second sequence, A-B4, occurs at least 30-50 times in the haploid human genome. In both cases the duplicated regions span relatively large segments of DNA.