||p.6710 right column bottom paragraph:"In longer experiments, the steady state was still not reached after 60 h (data not shown). Because, once transcription is maximal, a plateau should be reached within a few transcript half-lives (e.g., 75% of maximal expression should be achieved in two half-lives), the absence of an approach to equilibrium could indicate either a very long half-life for β-globin mRNA or a continuous increase in transcription. To address this issue, [investigators] measured the β-globin mRNA half-life in these HeLa tet-on cells by washing off doxycycline. A Northern blot analysis and the quantification of the corresponding signals using β-actin as an internal standard are presented in Fig. 3C and indicate a β-globin mRNA half-life of 13 h. Thus, the failure to reach equilibrium after 53 h of induction (i.e., four mRNA half-lives) suggested that transcription kept increasing for at least 2 days after induction by doxycycline."