Characterization of a cycloheximide-resistant Tetrahymena thermophila mutant which also displays altered growth properties.

A cycloheximide-resistant strain of Tetrahymena thermophila, expressing a mutant chx-B gene (Ares and Bruns, Genetics 90:463-474, 1978), displayed very different temperature-dependent growth characteristics than either wild-type cells or another cycloheximide-resistant strain expressing a different mutant gene. Whereas wild-type cells showed an immediate decline in ribosome translocation rates when shifted from 30 to 38 or 40 degrees C, this mutant strain (X-8) showed no such decline. These results directly correlated with the growth rate differences we found for these cells at these temperatures. By genetic analysis, we showed that the phenotype of cycloheximide resistance cosegregated with the ability to grow rapidly at 40 degrees C. Analyses, both direct and indirect, suggested that a number of functional and structural characteristics of the ribosomes from strain X-8 cells are most likely conformationally different from those of wild-type ribosomes.