BEYOND RIBOSOMAL DNA - ON TOWARDS THE TELOMERE

We have sequenced and analyzed 8.3 kb of sequence adjacent and distal to the human ribosomal DNA (rDNA); this distal sequence connects to th e rDNA cluster just 4 kb upstream of the first promoter and is shared among the acrocentric chromosomes and, at least in part, it is also pr esent in other primates. The sequence differs in character from that o f the rDNA intergenic spacer (IGS) in that it does not contain long st retches of either polypyrimidine or polypurine. However, just like the IGS, it contains numerous repetitive elements, including retroposed f ragments of 28S rRNA and large pieces of the IGS. In addition, we show that the rDNA clusters are not interrupted by other sequences and do not recombine with this distal segment.