Suppression of E6-ACHEmRNA levels under PMA. Presented is a semiquantitative kinetic follow-up of RT-PCR amplification of cell cultures RNA. Later appearance of ACHEmRNA-derived products reflects lower levels (by approximately eightfold for a three cycle difference3 ). Continuous decrease in the level of E6 ACHEmRNA caused progressively later appearance of the corresponding PCR product of mRNA from cell cultures treated for 12 and 24 hours with PMA as compared with control cells. The appearance of actin mRNA products remained unchanged, excluding the possibility of total mRNA destruction. PCR cycle numbers at which samples were withdrawn are noted above.