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J Biol Chem, Vol. 273, Issue 51, 34222-34229, December 18, 1998
From the Department of Biochemistry, University of Utah School of
Medicine, Salt Lake City, Utah 84132
cDNAs for the Xenopus laevis
homologue of the endo/exonuclease FEN-1 (DNase IV) have been cloned
using a polymerase chain reaction strategy. Products were obtained from
two nonallelic Xenopus genes (xFEN-1a and xFEN-1b) that
differ from each other by 4.5% in amino acid sequence. Both are 80%
identical to mammalian FEN-1 proteins and 55% identical to the yeast
homologues. When expressed in Escherichia coli, the
Xenopus enzymes showed flap endonuclease activity, a unique
feature of this class of nucleases. In addition, expression from the
Xenopus cDNAs complemented the temperature and methyl
methanesulfonate sensitivity of a yeast rad27 deletion,
which eliminates the endogenous FEN-1 gene product. Antiserum raised
against xFEN-1 was used to show that the protein accumulates during the
middle and late stages of oogenesis, in parallel with other DNA
metabolic activities, and that it is localized to the oocyte nucleus.
Flap endonuclease activity was demonstrated in oocyte nuclear extracts,
and this was inhibited by the anti-xFEN-1 antiserum. The antiserum did
not inhibit the major oocyte 5'
Characterization of FEN-1 from Xenopus laevis
cDNA CLONING AND ROLE IN DNA METABOLISM
3' exonuclease activity. DNA
synthesis in oocyte extracts was blocked by the antiserum, and the
nature of this inhibition suggests that xFEN-1 may be part of a large
complex of replication factors. Chromatographic evidence was obtained
for the existence of a complex that forms during DNA synthesis and
includes proliferating cell nuclear antigen in addition to xFEN-1.
These observations support a critical role for xFEN-1 in DNA
replication, but indicate that another enzyme must be responsible for
the exonuclease function required for homologous recombination in
Xenopus oocytes.
Copyright © 1998 by The American Society for Biochemistry and Molecular Biology, Inc.
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