Strains expressed HSP42 (A, strain MML980) or RRP40 (B, strain MML957) under the control of the tetO2 promoter. Doxycycline (5 µg/ml) was added at time 0 to cultures growing exponentially at 25°C, or to cultures at 4 and 45 min after the shift to 37°C. In each case, aliquots were taken at time 0 and at successive times after adding doxycycline for total mRNA isolation and determination of the levels of the corresponding mRNA by Northern analysis. Graphics represent the evolution of experimentally determined relative RA on a log scale as a function of time for the representative experiment mean half-life values, and the standard deviations of a total of three independent experiments are also indicated. To determine these values, a linear regression of experimental data was calculated by considering only the initial points for which linearity was maintained. The upper panels show the Northern analyses of RA expressed under the respective own promoters in wild-type W303-1A cells growing at 25°C, after being shifted at time 0 to 37°C. U1 is included as the loading control. The Kruskal-Wallis statistical test was applied to show that the differences between the calculated half lives were significantly different from the others for time point 4 min (HSP42) and time 0 (RRP40) and not for the other cases.