Enhancer-mediated activation of a growth-regulated promoter.

We have demonstrated that the collagen alpha 2 type 1 promoter inserted in an expression vector, behaves as a growth-regulated promoter, which is consistent with previous observations that collagen synthesis is growth-regulated in vivo. In contrast, the activity of the H2-K or the simian virus 40 early promoters does not seem to be affected by the rate of cell proliferation. The insertion of a polyoma enhancer 5' or 3' to the collagen transcription unit activates the collagen alpha 2 type 1 promoter, by a threefold greater factor in slowly growing cells compared to cells growing exponentially. These results show that enhancers can also function in slowly proliferating cells and activate the normally low activity of a promoter in these cells.