Single copy sequences in galago DNA resemble a repetitive human retrotransposon-like family.

Galago DNA contains a few single copy sequences that are homologous to the human THE 1 family of repeats. Two of these galago loci have been isolated as genomic clones and their structures are compared to the THE 1 consensus sequence. Whereas the human sequence resembles a proretroviral transposon, the galago sequences provide no evidence for a proretroviral sequence organization. The two galago clones share a common repeat sequence, which is homologous to the U5 region of the THE 1 long terminal repeat. Immediately 3' to this repeat, each galago clone contains sequences that are homologous to mutually exclusive regions of the internal THE 1 sequence. Thus, the human THE 1 sequence can be represented as a mosaic of the two ancestrally related galago loci. The galago loci are transcribed in vivo, so that their conservation in the primate genome could be selected. Human THE 1 repeats apparently resulted by recruiting preexisting cellular sequences via a retrovirally mediated process.