CHROMOSOMAL LOCATIONS OF MAJOR TRANSFER-RNA GENE CLUSTERS OF XENOPUS-LAEVIS

In Xenopus laevis eight tRNA genes are located in a 3.18 kb tandemly r epeated unit. There are 150 copies of the unit at a single locus near the long arm telomere of one of the acrocentric chromosomes in the 14- 17 group. Two additional classes of tRNA gene-cotaining repeats have b een isolated (defined by clones p3.1 and p3.2) that have structures re lated to that of the 3.18 kb unit. Using in situ hybridization at the electron microscopic level, the p3.2 repeats are found clustered at a single locus in the subtelomeric region on one of the submetacentric c hromosomes, whereas the p3.1 repeats are clustered at a locus indistin guishable from that containing the 3.18 kb repeats. This suggests that these tDNA tandem repeats can diverge in sequence from each other wit hout being at distantly separated loci.