BETA-TUBULIN MUTATION SUPPRESSES MICROTUBULE DYNAMICS IN-VITRO AND SLOWS MITOSIS IN-VIVO

Microtubule (MT) dynamics vary both spatially and temporally within ce lls and are thought to be important for proper MT cellular function. B ecause MT dynamics appear to be closely tied to the guanosine triphosp hatase (GTPase) activity of beta-tubulin subunits, we examined the imp ortance of MT dynamics in the budding yeast S. cerevisiae by introduci ng a T107K point mutation into a region of the single beta-tubulin gen e, TUB2, known to affect the assembly-dependent GTPase activity of MTs in vitro. Analysis of MT dynamic behavior by video-enhanced different ial interference contrast microscopy, revealed that T107K subunits slo wed both the growth rates and catastrophic disassembly rates of indivi dual MTs in vitro. In haploid cells tub2-T107K is lethal; but in tub2- T107K/tub2-590 heterozygotes the mutation is viable, dominant, and slo ws cell-cycle progression through mitosis, without causing wholesale d isruption of cellular MTs. The correlation between the slower growing and shortening rates of MTs in vitro, and the slower mitosis in vivo s uggests that MT dynamics are important in budding yeast and may regula te the rate of nuclear movement and segregation. The slower mitosis in mutant cells did not result in premature cytokinesis and cell death, further suggesting that cell-cycle control mechanisms ''sense'' the mi totic slowdown, possibly by monitoring MT dynamics directly. (C) 1995 Wiley-Liss, Inc.