Structural analysis of interspersed repetitive polymerase III transcription units in human DNA

The nucleotide sequences of two cloned fragments of human DNA which function as templates for RNA polymerase III in vitro confirm their identities as members of the Alu family of human interspersed repetitive DNA sequences (1,2). The interspersed and repetitive nature of these sequences in the genome was demonstrated by hybridization of nick-translated DNA from one of these clones to total genomic DNA and to DNA of individual random clones from a lambda Ch4A-based human genomic library. Short, direct terminal repeats of non-conserved sequence flank the 300 nucleotide Alu family conserved sequence. Within the Alu family sequence is found a 40-nucleotide region which is directly repeated 135 nucleotides downstream. This 40 nucleotide sequence is found once in the murine B1 interspersed repetitive sequence family (8). This and other evidence indicates that the human Alu family resembles a partial duplication of the murine B1 sequence.