Nucleic Acids Research, Vol 26, Issue 15 3528-3535, Copyright © 1998 by Oxford University Press
AP Clements and MF Singer
Heterologous expression of human LINE-1 ORF2 in yeast yielded a single
polypeptide (Mr145 000) which reacted with specific antibodies and co-
purified with a reverse transcriptase activity not present in the host
cells. Various deletion derivatives of the ORF2 polypeptide were also
synthesized. Reverse transcriptase assays using synthetic polynucleotides
as template and primer revealed that ORF2 protein missing a significant
portion of the N-terminal endonuclease domain still retains some activity.
Deletion of the C-terminal cysteine-rich motif reduces activity only a
small amount. Three non-overlapping deletions spanning 144 amino acids just
N-terminal to the common polymerase domain of the ORF2 protein were
analyzed for their effect on reverse transcriptase activity; this region
contains the previously- noted conserved Z motif. The two deletions most
proximal to the polymerase domain eliminate activity while the third,
most-distal deletion had no effect. An inactive enzyme was also produced by
substitution of two different amino acids in a highly-conserved octapeptide
sequence, Z8, located within the region removed to make the deletion most
proximal to the polymerase domain; substitution of a third had no effect.
We conclude that the octapeptide sequence and neighboring amino acids in
the Z region are essential for reverse transcriptase activity, while the
endonuclease and cysteine-rich domains are not absolutely required.
ARTICLES
The human LINE-1 reverse transcriptase:effect of deletions outside the common reverse transcriptase domain
Laboratory of Biochemistry, National Cancer Institute, Building 37, Room 4A-01, Bethesda, MD 20892, USA.
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