Post-fusion incompatibility in Physarum polycephalum. The involvement of DNA

The lethal reaction following fusion of plasmodia of a sensitive and a killer strain of Physarum polycephalum could be prevented by the incorporation of 5-bromo-2'-deoxyuridine in both strains. This result suggests the involvement of transcription in the lethal reaction. Although under appropriate conditions fusion of the strains is not followed by a lethal reaction the fused plasmodium will behave as the killer strain after subculturing. At different times after fusion, DNA was isolated from a plasmodium in which visible lethal reaction was prevented and separated on CsCl gradients. Killer DNA remained intact but sensitive DNA was broken down, mainly from 8--11 h after fusion.