Dexamethasone-stimulated expression of a proviral copy of mouse mammary tumor virus env mRNA.

The kinetics of dexamethasone induction of mouse mammary tumor virus RNAs in a cell line (designated line 8) which contains a deleted proviral DNA has been examined. This DNA is an apparent reverse transcription product of the env mRNA. A detectable increase in the 3.8-kilobase RNA (mouse mammary tumor virus env mRNA) was present within 15 min after hormone addition. The 2.5-kilobase RNA detected previously during hormone induction studies was also observed in these cells. Both RNAs increased in concentration up to about 4 h after hormone addition and thereafter attained the steady-state level. Pr73env was detected by immunoprecipitation and appeared to be identical to bona fide Pr73env isolated from wild-type mouse mammary tumor virus-infected cells. An additional 5.7 kilobases of RNA was detected in augmented quantities after hormone addition, but the structure of this RNA is not known.