Integrated proviruses as probes for chromosomal position effects in mammalian cells and their hybrids.

Proviruses are susceptible to transcriptional regulation by cellular influences operating at their integration sites. Two experimental systems have been exploited to analyse such chromosomal position effects but have identified contrasting molecular mechanisms. We propose a reconciliation of these apparently paradoxical results and suggest ways in which proviruses may serve as sensors for the further analysis of normal mammalian gene regulatory mechanisms.