Mammalian endo-exonuclease activity and its level in various radiation sensitive cell lines

The levels of endo-exonuclease in various mammalian cell lines were examined. While the expression of the endo-exonuclease during cell growth behaved exactly the same as the pattern observed in lower eukaryotes, the amount of activity was found to be reduced in the radiosensitive Chinese hamster ovary (CHO) xrs-5 and various human AT, AT-5 and NE-1 cells when compared to the radionormal CHO K1 and human HeLa cell lines. The reduced endo-exonuclease activity in these cells was due to a decreased amount of protein as demonstrated with the immuno-blot method. The results presented here suggest that endo-exonuclease may be one of the many proteins whose expression is regulated by genes coding for xrs-5 in CHO and AT in humans.