Delayed de novo methylation in teratocarcinoma suggests additional tissue-specific mechanisms for controlling gene expression.

Retrovirus infection of embryonal carcinoma cells is blocked at the level of provirus transcription. De novo methylation of the input provirus occurs in embryonal carcinoma cells but not in permissive, differentiated teratocarcinoma. The kinetics of proviral methylation in embryonal carcinoma cells, however, suggest that while methylation may have an important maintenance role in controlling gene expression, additional mechanisms are used by the early embryo to initiate negative gene expression.