Mal3, the fission yeast homologue of the human APC-interacting protein EB-1 is required for microtubule integrity and the maintenance of cell form.
Through a screen designed to isolate novel fission yeast genes required for chromosome segregation, we have identified mal3+. The mal3-1 mutation decreased the transmission fidelity of a nonessential minichromosome and altered sensitivity to microtubule-destabilizing drugs. Sequence analysis revealed that the 35-kD Mal3 is a member of an evolutionary conserved protein family. Its human counterpart EB-1 was identified in an interaction screen with the tumour suppressor protein APC. EB-1 was able to substitute for the complete loss of the mal3+ gene product suggesting that the two proteins might have similar functions. Cells containing a mal3 null allele were viable but showed a variety of phenotypes, including impaired control of cell shape. A fusion protein of Mal3 with the Aequorea victoria green fluorescent protein led to in vivo visualization of both cytoplasmic and mitotic microtubule structures indicating association of Mal3 with microtubules. The absence of Mal3 protein led to abnormally short, often faint cytoplasmic microtubules as seen by indirect antitubulin immunofluorescence. While loss of the mal3+ gene product had no gross effect on mitotic spindle morphology, overexpression of mal3+ compromised spindle formation and function and led to severe growth inhibition and abnormal cell morphology. We propose that Mal3 plays a role in regulating the integrity of microtubules possibly by influencing their stability.
Beinhauer
J D
JD
Institut für Mikrobiologie und Molekularbiologie, Justus-Liebig-Universität Giessen, 35392 Giessen, Germany.
Hagan
I M
IM
Hegemann
J H
JH
Fleig
U
U
D011125:Adenomatous Polyposis Coli; D025601:Adenomatous Polyposis Coli Protein; D000595:Amino Acid Sequence; D002455:Cell Division / Q000235:genetics / Q000502:physiology; D048429:Cell Size / Q000235:genetics / Q000502:physiology; D003001:Cloning, Molecular; D015169:Colony Count, Microbial; D017124:Conserved Sequence; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000502:physiology; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D017353:Gene Deletion; D015966:Gene Expression Regulation, Fungal; D006801:Humans; D007399:Interphase / Q000235:genetics; D008869:Microtubule-Associated Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D008870:Microtubules / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D005810:Multigene Family; D009154:Mutation; D010641:Phenotype; D012568:Schizosaccharomyces / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D029702:Schizosaccharomyces pombe Proteins; D017386:Sequence Homology, Amino Acid; D008941:Spindle Apparatus / Q000235:genetics / Q000502:physiology
D025601:Adenomatous Polyposis Coli Protein; D003598:Cytoskeletal Proteins; D005656:Fungal Proteins; C108851:Mal3 protein, S pombe; D008869:Microtubule-Associated Proteins; D029702:Schizosaccharomyces pombe Proteins