Clustered Arrangement of tRNA Genes of Xenopus laevis
This extract was created in the absence of an abstract.
Excerpt
Ribosomal DNA and 5 S DNA of Xenopus laevis share the interesting common feature that the cistrons within each are linked in tandem, separated by spacer DNA of regular size but unknown function. These units of cistron and spacer DNA are serially repeated many times in chromosomal DNA, but those of rDNA and 5 S DNA differ both in location and in the ratio of cistron to spacer sequence which they contain. All the rDNA is clustered at the nucleolus organizer, and it contains approximately equal amounts of spacer DNA and 28 S and 18 S RNA cistrons (cf. Birnstiel et al., 1971). In contrast, the spacer within 5 S DNA is about 5 times as long as the cistron (Brown et al., 1971), and 5 S DNA is clustered in separate linkage groups at the telomeres of probably all of the 18 chromosome pairs of Xenopus (Pardue et al.,
