Sequences of Human Repetitive DNA, Non-α-globin Genes, and Major Histocompatibility Locus Genes
I. Repeated-sequence DNA
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Excerpt
I. REPEATED-SEQUENCE DNA
The first category of interspersed, repetitive human DNA to be clearly defined at the sequence level is the so-called Alu family, which consists of 300-nucleotide DNA segments showing 75–85% homology with one another and interspersed almost randomly on the human genome. In total, there are about 300,000–500,000 copies of the Alu family in the human genome. Most copies of these sequences contain polymerase III promoters that are active in vitro. The transcription begins at one end of the repetitive element and extends across the repeat for varying distances into flanking DNA. In addition, most copies of the Alu family are flanked by direct repeats of non-Alu DNA. These features led to the proposal that the Alu families are transposable DNA elements with transposition mediated by their RNA transcripts (Jagadeeswaran et al. 1981a,b, 1982b; van Arsdell et al. 1981). Several observations on nucleotide sequences confirm the presumption that...
