The genome of the THE I human transposable repetitive elements is composed of a basic motif homologous to an ancestral immunoglobulin gene sequence.

Amplification of rearranged human immunoglobulin heavy-chain genes using the polymerase chain reaction resulted unexpectedly in the amplification of human transposable repetitive element genomes. These were identified as members of the THE I (transposon-like human element I) transposable element family. Analysis of the THE I sequences revealed the presence of several copies of the ancestral building block described > 10 years ago by Ohno and coworkers as the primordial immunoglobulin sequence. The frequency and degree of homology of the repeats of the basic unit were similar for the two genes, as well as for two murine intracisternal A particles. These findings suggest that both the transposable genetic elements and the immunoglobulin genes originated from a common ancestral building block.