Modulation of tubulin polypeptide ratios by the yeast protein Pac10p.
Normal assembly and function of microtubules require maintenance of the proper levels of several proteins, including the tubulin polypeptides themselves. For example, in yeast a significant excess of beta-tubulin causes rapid microtubule disassembly and subsequent cell death. Even the modest excess of beta-tubulin produced by genetic alterations such as deletion of the minor alpha-tubulin gene TUB3 affects cell growth and can confer microtubule phenotypes. We show here that the levels of the yeast protein Pac10p affect the relative levels of the tubulin polypeptides. Cells deleted for PAC10 have the same phenotypes as do cells that express reduced levels of alpha-tubulin or Rbl2p, two proteins that bind beta-tubulin. Conversely, overexpression of Pac10p enhances the ability of alpha-tubulin or Rbl2p to suppress the lethality associated with excess beta-tubulin. However, Pac10p is itself not a beta-tubulin binding protein. Pac10 null cells show a 30% decrease in the ratio of alpha-tubulin to beta-tubulin. The results suggest that Pac10p modulates the level of alpha-tubulin in the cell, and so influences microtubule morphogenesis and tubulin metabolism.
Alvarez
P
P
Department of Biology and Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Smith
A
A
Fleming
J
J
Solomon
F
F
D003001:Cloning, Molecular; D004722:Endoribonucleases; D005656:Fungal Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D017353:Gene Deletion; D005800:Genes, Fungal / Q000502:physiology; D005804:Genes, Lethal / Q000235:genetics; D016547:Kinesins; D008869:Microtubule-Associated Proteins; D008870:Microtubules / Q000235:genetics / Q000378:metabolism; D016296:Mutagenesis; D010455:Peptides / Q000378:metabolism*; D010641:Phenotype; D012441:Saccharomyces cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014404:Tubulin / Q000235:genetics*
C075342:CIN8 protein, S cerevisiae; D005656:Fungal Proteins; D008869:Microtubule-Associated Proteins; D010455:Peptides; D029701:Saccharomyces cerevisiae Proteins; D014404:Tubulin; D004722:Endoribonucleases; C499539:PAC1 protein, S cerevisiae; D016547:Kinesins