Analysis of a mutant expressing temperature-sensitive changes of cell size in Tetrahymena.

A temperature-sensitive mutant of Tetrahymena expresses an increase in cell volume by a factor of 2.5 upon shift to restrictive temperature. Cellular amounts of protein, RNA, and DNA increase at roughly the same proportions. The mutant cell size is attained by cessation of divisions immediately after temperature shift for a period of time which is about equal to one generation time. During this time cell growth and DNA replication continue at virtually unchanged rates. Maintained at the restrictive temperature the mutant cells divide at the same rate as the wild-type cells. Upon return to the permissive temperature, cell size is reduced by the combined effects of an accelerated division rate together with a decelerated growth rate.