Localization of three DNA segments encompassing tRNA genes to human chromosomes 1, 5, and 16: proposed mechanism and significance of tRNA gene dispersion.

The chromosomal locations of three cloned human DNA fragments encompassing tRNA genes have been determined by Southern analysis of human-rodent somatic cell hybrid DNAs with subfragments from these cloned genes and flanking sequences used as hybridization probes. These three DNA segments have been assigned to human chromosomes 1, 5, and 16, and homologous sequences are probably located on chromosome 14 and a separate locus on chromosome 1. These studies, combined with previous results, indicate that tRNA genes and pseudogenes are dispersed on at least seven different human chromosomes and suggest that these sequences will probably be found on most, if not all, human chromosomes. Short (8-12 nucleotide) direct terminal repeats flank many of the dispersed tRNA genes. The presence of these flanking repeats, combined with the dispersion of tRNA genes throughout the human genome, suggests that many of these genes may have arisen by an RNA-mediated retroposition mechanism. The possible functional significance of this gene dispersion is considered.