ABSTRACT
The genome of living organisms is subject to a continuous threat from the environment. Chemical and physical carcinogens, toxic compounds, and infectious agents may cause significant alterations in the chemical structure and organization of the genetic material. Transient changes in genome stability and altered patterns of gene expression in carcinogen–treated cells suggest that the exposure to carcinogens leads to major perturbations in cellular control processes. Upon exposure to genotoxic compounds, such a relaxation may be needed to allow the action of repair mechanisms and prevent the loss of important genetic information. The altered patterns of SV40 replication and gene expression following carcinogen treatment suggest that exposure to carcinogens may cause increased permissivity to SV40 development in a hitherto semipermissive environment. The expression of the cellular dhfr gene was measured using fluorescent methotrexate. Specific characteristics of carcinogen–induced gene expression are shared with the lytic behavior of the SV40 genome in a permissive environment.
