Fate of exogenous mouse DNA in chicken fibroblasts in vitro: Non-conservative preservation

Abstract

Monolayers of chicken embryo cells were cultivated for 24 h in the presence of mouse [ 3H]DNA and bromo[ 14C]deoxyuridine. The cells were lysed and subjected to CsCl density gradient analysis. Newly synthesized cellular DNA was both density and 3H labeled, and banded in two peaks formed, respectively, by “heavy-light” and “heavy-heavy” stranded molecules whose 3H label corresponded to donor DNA reutilized at the precursor level. A significant amount of donor DNA, equivalent to 2 % of the recipient cell genome, escaped degradation in the recipient cell environment and banded in the region of light density. This DNA, rebanded under alkaline conditions, showed a shift towards higher density, proving that density label was introduced into extant donor DNA strands. The shift was lacking when bromodeoxyuridine-prelabeled recipient cells were incubated with donor DNA in the absence of density label. Thus, donor DNA molecules did not attach end-to end to recipient DNA. The formation of non-conservative material being associated with the recipient cell DNA synthesis suggests that recombination events took place between donor and newly synthesized recipient DNA strands.