The microtubule plus end-tracking proteins mal3p and tip1p cooperate for cell-end targeting of interphase microtubules.
BACKGROUND
CLIP-170 and EB1 protein family members localize to growing microtubule tips and link spatial information with the control of microtubule dynamics. It is unknown whether these proteins operate independently or whether their actions are coordinated. In fission yeast the CLIP-170 homolog tip1p is required for targeting of microtubules to cell ends, whereas the role of the EB1 homolog mal3p in microtubule organization has not been investigated.


RESULTS
We show that mal3p promotes the initiation of microtubule growth and inhibits catastrophes. Premature catastrophes occur randomly throughout the cell in the absence of mal3p. mal3p decorates the entire microtubule lattice and localizes to particles along the microtubules and at their growing tips. Particles move in two directions, outbound toward the cell ends or inbound toward the cell center. At cell ends, the microtubule tip-associated mal3p particles disappear followed by a catastrophe. mal3p localizes normally in tip1-deleted cells and disappears from microtubule tips preceding the premature catastrophes. In contrast, tip1p requires mal3p to localize at microtubule tips. mal3p and tip1p directly interact in vitro.


CONCLUSIONS
mal3p and tip1p form a system allowing microtubules to target cell ends. We propose that mal3p stimulates growth initiation and maintains growth by suppressing catastrophes. At cell ends, mal3p disappears from microtubule tips followed by a catastrophe. mal3p is involved in recruiting tip1p to microtubule tips. This becomes important when microtubules contact the cell cortex outside the cell ends because mal3p dissociates prematurely without tip1p, which is followed by a premature catastrophe.
Busch
Karl Emanuel
KE
European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
Brunner
Damian
D
D002352:Carrier Proteins / Q000378:metabolism*; D017931:DNA Primers; D005455:Fluorescent Antibody Technique; D006023:Glycoproteins / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D006360:Heat-Shock Proteins; D007381:Intermediate Filament Proteins; D007399:Interphase / Q000502:physiology*; D008164:Luminescent Proteins; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism* / Q000502:physiology; D011233:Precipitin Tests; D011485:Protein Binding / Q000502:physiology; D012568:Schizosaccharomyces; D029702:Schizosaccharomyces pombe Proteins / Q000378:metabolism*; D014741:Video Recording
D002352:Carrier Proteins; D017931:DNA Primers; D006023:Glycoproteins; D006360:Heat-Shock Proteins; D007381:Intermediate Filament Proteins; D008164:Luminescent Proteins; C108851:Mal3 protein, S pombe; D008869:Microtubule-Associated Proteins; D029702:Schizosaccharomyces pombe Proteins; C114142:tip1 protein, S pombe; D049452:Green Fluorescent Proteins