Amplification of the rRNA Genes in Tetrahymena
This extract was created in the absence of an abstract.
Excerpt
The genes coding for rRNA are normally present in several hundred copies in eukaryotic genomes. These sequences are generally arranged in tandemly repeated arrays and are located in one or a few specific regions of the chromosome set. In some organisms, however, extrachromosomal rDNA has also been found. For instance, in the oocyte of Xenopus, where it has been best studied, over a million copies of extrachromosomal rDNA are present as a result of gene amplification. The organization and replication of these extrachromosomal genes has been well characterized, but the mechanism by which they are generated still remains unknown.
Recently, extrachromosomal rDNA has been detected in a few simple eukaryotes, including the ciliated protozoan Tetrahymena. Tetrahymena normally contains a macronucleus and a micronucleus in each cell. The rDNA in the macronucleus was previously shown to replicate on a different time schedule from the rest of the nuclear DNA, either during...
