Localization of 5S RNA genes on chromosomes of plethodontid salamanders

The chromatin structure of the oocyte-type 5S RNA genes in Xenopus laevis was investigated. Blot hybridization analysis of DNA from micrococcal nuclease digests of erythrocyte nuclei showed that 5S DNA has the same average nucleosome repeat length, 192 +/- 4 base pairs, as two Xenopus satellite DNAs and bulk erythrocyte chromatin. The positions of nuclease-sensitive regions in the 5S DNA repeats of purified DNA and chromatin from erythrocytes were mapped by using an indirect end-labeling technique. Although most of the sites cleaved in purified DNA were also cleaved in chromatin, the patterns of intensities were strikingly different in the two cases. In 5S chromatin, three nuclease-sensitive regions were spaced approximately a nucleosome length apart, suggesting a single, regular arrangement of nucleosomes on most of the 5S DNA repeats. The observed nucleosome locations are discussed with respect to nucleotide sequences known to be important for expression of 5S RNA. Because the preferred locations appear to be reestablished in each repeating unit, despite spacer length heterogeneity, we suggest that the regular chromatin structure reflects the presence of a sequence-specific DNA-binding component on inactive 5S RNA genes.

Download Full-text

Pseudogene structure in 5S RNA genes

Nature ◽

10.1038/271205a0 ◽

1978 ◽

Vol 271 (5642) ◽

pp. 205-206 ◽

Cited By ~ 3

Author(s):

Peter Ford

Keyword(s):

5S Rna ◽

5S Rna Genes ◽

Rna Genes

Download Full-text

Differential order of replication of Xenopus laevis 5S RNA genes

Molecular and Cellular Biology ◽

10.1128/mcb.6.7.2536-2542.1986 ◽

1986 ◽

Vol 6 (7) ◽

pp. 2536-2542

Author(s):

D R Guinta ◽

L J Korn

Keyword(s):

Xenopus Laevis ◽

Rna Replication ◽

S Phase ◽

Cold Spring Harbor ◽

5S Rna ◽

Expression Model ◽

Cold Spring ◽

5S Rna Genes ◽

Equilibrium Centrifugation ◽

Rna Genes

In Xenopus laevis there are two multigene families of 5S RNA genes: the oocyte-type 5S RNA genes which are expressed only in oocytes and the somatic-type 5S RNA genes which are expressed throughout development. The Xenopus 5S RNA replication-expression model of Gottesfeld and Bloomer (Cell 28:781-791, 1982) and Wormington et al. (Cold Spring Harbor Symp. Quant. Biol. 47:879-884, 1983) predicts that the somatic-type 5S RNA genes replicate earlier in the cell cycle than do the oocyte-type genes. Hence, the somatic-type 5S RNA genes have a competitive advantage in binding the transcription factor TFIIIA in somatic cells and are thereby expressed to the exclusion of the oocyte-type genes. To test the replication-expression model, we determined the order of replication of the oocyte- and somatic-type 5S RNA genes. Xenopus cells were labeled with bromodeoxyuridine, stained for DNA content, and then sorted into fractions of S phase by using a fluorescence-activated cell sorter. The newly replicated DNA containing bromodeoxyuridine was separated from the lighter, unreplicated DNA by equilibrium centrifugation and was hybridized with DNA probes specific for the oocyte- and somatic-type 5S RNA genes. In this way we found that the somatic-type 5S RNA genes replicate early in S phase, whereas the oocyte-type 5S RNA genes replicate late in S phase, demonstrating a key aspect of the replication-expression model.

Download Full-text