Evidence for inactivation of DNA repair in frozen and thawed mammalian cells.

A variety of cell strains and lines were frozen and thawed by conventional techniques for cell storage. Following thawing, extracts of cells were prepared and incubated with UV-irradiated E. coli DNA. Thymine dimer excision activity present in extracts of unfrozen cells was lost in extracts of recently thawed cells. The ability to exercise dimers was restored after about 40 h post-thawing, but the recovery was inhibited if cells were cultured in the presence of puromycin. Correlating with the loss of dimer excising activity there was a reduced cell viability as measured by trypan blue dye exclusion.