MAMMALIAN ENDO-EXONUCLEASE ACTIVITY AND ITS LEVEL IN VARIOUS RADIATION-SENSITIVE CELL-LINES

The levels of endo-exonuclease in various mammalian cell lines were ex amined, While the expression of the endo-exonuclease during cell growt h 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 lin es, The reduced endo-exonuclease activity in these cells was due to a decreased amount of protein as demonstrated with the immuno-blot metho d. The results presented here suggest that endo-exonuclease may be one of the many proteins whose expression is regulated by genes coding fo r xrs-5 in CHO and AT in humans.