Synthesis of the serotype H3 (SerH3) surface antigen is temperature dependent 
and responds within 1 h to a change in incubation conditions (G.A. Bannon, R. 
Perkins-Dameron, and A. Allen-Nash, Mol. Cell. Biol. 6:3240-3245, 1986). 
Recently, a Tetrahymena thermophila cDNA clone (pC6; D.W. Martindale and P.J. 
Bruns, Mol. Cell. Biol. 3:1857-1865, 1983) has been shown to be homologous to a 
portion of the SerH3 mRNA (F.P. Doerder and R.L. Hallberg, personal 
communication), and it was shown that the cellular levels of this RNA rapidly 
decreased when cells were shifted from 30 to 41 degrees C (R.L. Hallberg, K.W. 
Kraus, and R.C. Findly, Mol. Cell. Biol. 4:2170-2179, 1984). These observations 
indicate that synthesis of the SerH3 protein is highly regulated in response to 
temperature and led us to initiate studies to determine the mechanism(s) by 
which SerH3 gene expression is controlled. Using pC6 as a hybridization probe 
for the SerH3 mRNA, we have determined that (i) the level of SerH3 protein 
synthesis is directly correlated with the amount of SerH3 message available for 
translation; (ii) there is, at most, a twofold difference between the relative 
transcription rates of SerH3 genes at 30 and 40 degrees C; (iii) the SerH3 mRNA 
half-life in cells incubated at 30 degrees C is greater than 1 h, whereas the 
half-life in cells incubated at 40 degrees C is only approximately 3 min. These 
results demonstrate that Tetrahymena SerH3 surface protein expression is 
regulated by mRNA abundance. Furthermore, the major mechanism controlling mRNA 
abundance is a dramatic temperature-dependent change in SerH3 mRNA stability.