The human 5S rRNA genes are found in clusters of tandem repeated units. We have cloned and partially characterized six restriction fragments from two clusters of 2.3 kb and 1.6 kb repeats, respectively. Four fragments from the cluster of 2.3 kb repeats contain a 5S rRNA gene and one fragment contains a gene variant with an additional nucleotide in the internal control region. A fragment from the 1.6 kb cluster contains a gene and is highly homologous to the 2.3 kb repeats, except for a large deletion in the 3'-flanking region starting 12 bp downstream of the gene. The number of genes and closely related gene variants is found to be 300-400 per haploid human genome. 100-150 of these are found in 2.3 kb repeats and 5-10 are found in 1.6 kb repeats. The total number of 5S rRNA sequences, including pseudogenes, is 1700-2000 per haploid genome. The genes and the gene variant are transcribed equally efficient in a HeLa cell extract. If 5'-flanking sequences, including a GC-motif in the -40 region, are removed from the genes, transcription is reduced with a factor 10 or more, suggesting that sequences upstream of the coding region are important for the level of transcription.

No abstract

No abstract

The bona fide 5S rRNA genes in the rat are found in a 1.8-kb tandem repeat and the pseudogenes occur in a 2.5-kb tandem repeat. Three bona fide 5S rRNA genes and one gene variant with one base substitution in the coding region were isolated from the 1.8-kb repeat. Six pseudogenes were isolated from the 2.5-kb repeat. The total number of genes/gene variants/pseudogenes is 700–1200 copies per haploid genome, and the pseudogene repeat contains about 50% more 5S rDNA related sequences compared with the bona fide gene repeat. Various well-defined 5’- and 3’-flanking sequences of the bona fide gene and of the pseudogene were used for in situ hybridization to metaphase chromosomes. The results showed that the bona fide 5S rRNA gene repeat Rn5s maps to chromosome 19ql2 and the pseudogene repeat Rn5sp maps to 12ql2.

No abstract