Two additional potential retrotransposons isolated from a human L1 subfamily that contains an active retrotransposable element.

We have previously reported the isolation of a human retrotransposable L1 element. This element, allele L1.2B at the LRE-1 locus of chromosome 22, was shown by nucleotide sequence identity to be the direct precursor of a de novo retrotransposition event into the factor VIII gene on the X chromosome, resulting in hemophilia A in patient JH-27. We now report the isolation of the two remaining full-length members of the subfamily of L1 elements closely related to L1.2B present in the genome of the mother of JH-27. Since these elements, L1.3 and L1.4, are very similar in sequence to L1.2B and contain both open reading frames 1 and 2 intact, they are also likely to be active retrotransposable elements. This suggests that certain L1 subfamilies may contain multiple active elements.