Abstract
We used HeLa cells as recipients in a gene transfer assay to characterize DNA sequences that negatively regulate mammalian cell growth. In this assay, genomic DNA from quiescent human embryo fibroblasts was more inhibitory for HeLa replication than was DNA from either Escherichia coli or HeLa cells. Surprisingly, growth inhibitory activity depended on the growth state of the cells from which genomic DNA was prepared; it was strongest in DNA prepared from serum-deprived, quiescent embryo fibroblasts. This latter observation implies a role for DNA modification(s) in regulating the activity of the inhibitory sequences detected in our assay. The level of the observed growth inhibitory activity was sometimes high, suggesting that the relevant sequences may be abundantly represented in the mammalian genome. We speculate that these findings may provide new insights into the molecular mechanisms involved in cellular quiescence and in vitro senescence.