Purification and characterization of two transcribed repetitive DNA fractions from the pigeon genome.

Two fractions of the repeats belonging to intermediate frequency repetitive DNA were isolated from the total pigeon nuclear DNA fragmented to about 450 nucleotides. One fraction was designated as "rare repeats" (repetition frequency about 35 per haploid genome) and another termed as "moderate repeats" (repetition frequency about 2500 per haploid genome). The rare repeats, which constitute about 7% of the total DNA, include at least 75% of the repetitive DNA sequences transcribed into the high molecular fraction (greater than 45S) of HnRNA in erythroid cells. These repeats have properties compatible with the characteristics of the class of low frequency interspersed DNA found in genomes of many other Metazoan species. The moderate repeats contribute only about 10-20% of the total repetitive DNA copies present in greater than 45S HnRNA and differ from the rare repeats in some other properties.--The possible role of the rare repeats in the genome is discussed.