Y. Nakagawa et al., CDNA CLONING, SEQUENCE-ANALYSIS AND EXPRESSION OF A MOUSE 44-KDA NUCLEAR-PROTEIN COPURIFIED WITH DNA-REPAIR FACTORS FOR ACID-DEPURINATED DNA, Acta medica Okayama, 51(4), 1997, pp. 195-206
We purified a 44-kDa nuclear protein from salt-extract of permeable mo
use ascites sarcoma cells in an effort to isolate factors involved in
the repair of acid-depurinated DNA. It was copurified with a major AP
endonuclease (APEX nuclease) by sequential column chromatography then
further purified by sodium dodecyl sulphate-polyacrylamide gel electro
phoresis as a possible DNA repair support factor. Its partial amino ac
id sequences were determined, and a cDNA clone for the protein was iso
lated from a mouse T-cell cDNA library using long degenerate oligonucl
eotide probes deduced from the amino acid sequence. The complete nucle
otide sequence of the cDNA (1.7 kilobases) was determined. Northern hy
bridization using this cDNA detected two transcripts: 1.8 kb being the
major one and 2.6 kb being the minor one. The complete amino acid seq
uence for the protein predicted from the nucleotide sequence of the cD
NA indicates that the 44-kDa protein consists of 394 amino acids with
a calculated molecular weight of 43,698. In tests performed thus far,
the recombinant 44-kDa protein expressed in Escherichia coli has not e
xpressed any repair-support activity. It remains to be analyzed whethe
r the protein attains this activity after appropriate posttranslationa
l modifications. Most parts of the 44-kDa protein cDNA and the deduced
amino acid sequence were found to be identical to those of the protei
n p38-2G4, recently reported as a cell cycle-specifically modulated nu
clear protein of 38 kDa. The p38-2G4 may be a truncated form of the pr
esent 44-kDa protein.