Identification and mapping of type 1 neurofibromatosis (NF1) homologous loci

During the establishment of a YAC contig for the type 1 neurofibromatosis (NF1) region on human chromosome 17q11.2, several YAC clones were isolated which originated from a different chromosome but which retained strong homology to NF1 coding regions (Marchuk et al., 1992). Fluorescence in situ hybridization (FISH) using these clones has identified NF1-homologous loci on several human chromosomes, including 2, 14, 15, 21, and 22. PCR amplification using primers originally designed to amplify NF1 exons has confirmed these chromosome localizations and, in addition, has revealed NF1-homologous sequences on chromosomes 12 and 20. Sequence analysis of the amplified products has demonstrated that (1) most of these loci have > 90% identity with NF1 sequences; (2) most of these loci represent nonprocessed pseudogenes; and (3) for the chromosome 12 locus, the two described regions of homology with NF1 have open reading frames. Finally, we have identified two novel alpha-satellite DNA repeat units in proximity to NF1-homologous sequences on chromosome 14. Their association suggests a mechanism for dispersion of the NF1-homologous loci based on alpha-satellite-mediated exchange between nonhomologous chromosomes.