Cloned extrachromosomal circular DNA copies of the human transposable element THE-1 are related predominantly to a single type of family member.

The 2300 base-pair transposon-like human element, THE-1, has been identified in the extrachromosomal circular DNA of the established human cell line HeLa as a relatively homogeneous population of covalently closed 1900 base-pair molecules. THE-1, which has been classified tentatively as a retroviral-like transposable element (a retrotransposon), is present in the extrachromosomal circular DNA of African green monkey (BSC-1) and human lymphoblastoid (Jurkat) cell lines. The 1900 base-pair extrachromosomal elements isolated and cloned from HeLa cells (1) appear to contain only THE-1-specific nucleotide sequences, (2) are circularized versions of the linear chromosomal sequence, and (3) are related predominantly to a single, or single type of, family member.