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PubMed1991

Isolation of an active human transposable element.

Two de novo insertions of truncated L1 elements into the factor VIII gene on the X chromosome have been identified that produced hemophilia A. A full-length L1 element that is the likely progenitor of one of these insertions was isolated by its sequence identity to the factor VIII insertion. This L1 element contains two open-reading frames and is one of at least four alleles of a locus on chromosome 22 that has been occupied by an L1 element for at least 6 million years.

Alleles↗

PubMed1991

Reverse transcriptase encoded by a human transposable element.

L1 elements are highly repeated mammalian DNA sequences whose structure suggests dispersal by retrotransposition. A consensus L1 element encodes a protein with sequence similarity to known reverse transcriptases. The second open reading frame from the human L1 element L1.2A was expressed as a fusion protein targeted to Ty1 virus-like particles in Saccharomyces cerevisiae and shown to have reverse transcriptase activity. This activity was eliminated by a missense mutation in the highly conserved amino acid motif Y/F-X-D-D. Thus, L1 represents a potential source of the reverse transcriptase activity necessary for dispersion of the many classes of mammalian retroelements.

Base Sequence↗

PubMed1989

Characterization of a nondeleterious L1 insertion in an intron of the human factor VIII gene and further evidence of open reading frames in functional L1 elements.

We have characterized an insertional event in IVS-10 of the factor VIII gene in a pedigree containing a hemophilia A patient (JH-25). The inserted DNA is a 5' truncated L1 element that is 681 bp long followed by a 3'66-bp poly(A) tract. The L1 element is inserted 154 bp 5' to the start of exon 11 and is flanked by a 13- to 17-bp target site duplication. The L1 insertion is present in four generations of the patient's family. The maternal grandfather who carries the insertion does not have hemophilia A, indicating that the insertion is not the cause of hemophilia A in the patient. We have sequenced this insertion and two previously reported de novo L1 insertions in the factor VIII gene in patients JH-27 (3785 bp) and JH-28 (2132 bp). The three nucleotide sequences differ by 0.2-0.8%. All three of these L1 insertions have open reading frames (ORFs) (1192, 642, and 157 aa) and the three derived amino acid sequences are 98-99% identical. The previously reported sequence similarity between L1 3' ORFs and the polymerase domain of reverse transcriptases is maintained in the ORFs of the JH-27 and JH-28 L1 insertions. The presence of open reading frames and the close sequence similarity of these recently inserted L1 elements provide indirect evidence for the existence of a set of functional L1 elements that encode one or more proteins necessary for their retrotransposition.

Base Sequence↗