The c-fos proto-oncogene was discovered by homology to transforming viral genes, leading to speculation that transforming viruses had captured a cellular gene involved in cell cycle control. Indeed overexpression of c-Fos protein led to deregulated growth control, and c-Fos was thought to be so critically involved in cell cycle control that transcriptional transrepression of its own promoter was interpreted as a negative feedback mechanism. However, recent findings render this conclusion improbable, Fos transrepression being most parsimoniously explained as transcriptional squelching imposed by artificially elevated levels of exogenous Fos protein.