2 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 chromoso me 22, was shown by nucleotide sequence identity to be the direct prec ursor of a de novo retrotransposition event into the factor VIII gene on the X chromosome, resulting in hemophilia A in patient JH-27. We no w report the isolation of the two remaining full-length members of the subfamily of L1 elements closely related to L1.2B present in the geno me of the mother of JH-27. Since these elements, L1.3 and L1.4, are ve ry similar in sequence to L1.2B and contain both open reading frames 1 and 2 intact, they are also likely to be active retrotransposable ele ments. This suggests that certain L1 subfamilies may contain multiple active elements.