Cloning of the multifunctional rat apurinic/apyrimidinic endonuclease (rAPEN)/redox factor from an immature T cell line.

We have cloned a cDNA for the rat apurinic/apyrimidinic (AP) endonuclease DNA repair enzyme that, in humans, has also been shown to function as a redox protein, altering the reduction/ oxidation state of cFos protein (1). The cDNA was initially isolated by polymerase chain reaction (PCR) from the rat immature T cell line Nb2 (2), using oligonucleotides made to the mouse AP endonuclease (4). The oligonucleotides were located at the translation initiation and termination codons. Following the isolation and initial sequencing of this clone to verify that it was the rat AP endonuclease, it was used to screen a rat testis gtl 1 cDNA library. A cDNA of 1198 bp was isolated and sequenced in its entirity. The rat clone predicts an open reading frame of 316 amino acids with a predicted molecular weight of 35,371 D. The rat AP endonuclease has 85% DNA identity to the human (3) and 93 % to the mouse AP endonucleases (4). Amino acid identity between the rat and mouse is 97% at the amino acid level, while rat and human share 93% identical amino acids. The region surrounding the conserved cysteine at position 65 (hAPE) near the amino terminus is identical in all three proteins (rat, mouse and human). This cysteine has been shown to be crucial for the redox activity of this enzyme and resides in a domain separate from that required for the DNA