Rapid physical mapping of the human trk protooncogene (NTRK1) to human chromosome 1q21-q22 by P1 clone selection, fluorescence in situ hybridization (FISH), and computer-assisted microscopy.

Physical mapping of small genomic DNA fragments or expressed sequences by in situ hybridization is typically limited by the size of the target DNA sequence. Isolation of large insert DNA clones from libraries containing the target DNA sequence facilitates physical mapping by fluorescence in situ hybridization and allows rapid assignment of genes to cytogenetic bands. Here, we demonstrate the scheme by mapping the human protooncogene trk (NTRK1), a tyrosine kinase receptor type I gene that has earlier been assigned to two different cytogenetic loci. Large DNA insert library screening was carried out by in vitro DNA amplification using oligonucleotide primers flanking exon 4 of trk. The scheme presented here can easily be generalized to map physically very small nonrepetitive genomic DNA fragments or incomplete cDNAs.