THE ARABIDOPSIS-THALIANA APURINIC ENDONUCLEASE ARP REDUCES HUMAN TRANSCRIPTION FACTORS FOS AND JUN

An Arabidopsis thaliana cDNA encoding an analogue, referred to as Arp for apurinic endonuclease-redox protein, of the human redox factor REF has been cloned. Arp stimulates in vitro DNA-binding activity of the human transcription factors Jun and Fos by the reduction of a cysteine residue located in the DNA-binding domain. Based on amino acid sequen ce homology, this redox activity is probably confined to the small int ernal domain of the Arp protein. In analogy to REF, we show that the A rabidopsis Arp protein also functions as an apurinic/apyrimidinic clas s II endonuclease. This base-free endonuclease activity resides in the carboxyl-terminal domain, and this part of the protein has significan t sequence similarity to bacterial (Escherichia coli exonuclease III a nd Streptococcus pneumoniae exonuclease A) and animal (Drosophila Rrp1 and human REF/HAP) apurinic/apyrimidinic endonucleases. The amino-ter minal domain of the Arp protein is highly charged and apparently incre ases the affinity of the protein for DNA. Therefore, the Arabidopsis A rp protein is multifunctional and may be involved both in DNA repair a nd in the regulation of transcription.