ACT3: a putative centractin homologue in S. cerevisiae is required for proper orientation of the mitotic spindle.

Abstract

As part of our ongoing efforts to understand the functional role of vertebrate centractins, we have identified a new member of the actin- related family of proteins in the yeast Saccharomyces cerevisiae using a PCR-based approach. Consistent with the current nomenclature for actin-related proteins in yeast, we propose to denote this locus ACT3. The primary amino acid sequence of Act3p is most similar to canine and human alpha-centractin (73% similarity/54% identity). The sequence of a genomic clone indicates ACT3 lies adjacent to and is transcribed convergently with respect to FUR1 on chromosome VIII. Molecular genetic analysis indicates ACT3 is represented by a single gene from which the corresponding mRNA is expressed at a low level compared to ACT1. Tetrad analysis of heterozygotes harboring a TRP1 replacement of the ACT3- coding region indicates ACT3 is nonessential for growth under normal conditions and at extremes of temperature and osmolarity. However, growth at 14 degrees C indicates a spindle orientation defect similar to phenotypes recently described for yeast harboring mutations in actin, tubulin, or cytoplasmic dynein. Taken together, our data suggest that ACT3 is the S. cerevisiae homologue of vertebrate centractins.

Deletion of nudC, a nuclear migration gene of Aspergillus nidulans, causes morphological and cell wall abnormalities and is lethal.

“…Also needed are dynactin, * Corresponding author. a multiprotein complex required for dynein to mediate vesicle movement (Clark and Meyer, 1994;Muhua et al, 1994;Plamann et al, 1994;Robb et al, 1995;Bruno et al, 1996), and a functional microtubule track (Oakley and Morris, 1980;Sullivan and Huffaker, 1992).…”

Molecular and Functional Basis for the Scaffolding Role of the p50/Dynamitin Subunit of the Microtubule-associated Dynactin Complex

“…Initial genetic studies performed in yeast, filamentous fungi, and Drosophila demonstrated that dynactin was an obligate cofactor of the dynein motor (3)(4)(5)(6). To date, many functional studies confirmed that the dynactin complex is required for most, if not all, dynein-based cellular processes (reviewed in Ref.…”

“…1) as follows: (i) the Arp1 rod, consisting of a short polymer of eight copies of Arp1 (actin-related protein-1), capped on its positive barbed end by the CapZ ␣/␤ heterodimer and on its negative pointed end by a heterotetrameric complex containing Arp11, p25, p27, and p62; and (ii) the shoulder/sidearm, emanating from the barbed end, composed of the p24, p50/dynamitin (DM), 3 and p150 Glued subunits, the latter protruding from the shoulder as a flexible extension (7). Although the Arp1 rod is most likely responsible for dynactin recruitment to the surface of several subcellular structures, the extended sidearm links the complex to both dynein and microtubules.…”

Interdependence of Filamentous Actin and Microtubules for Asymmetric Cell Division

“…Mutations in both the dynactin complex (Li et al, 1993;McMillan and Tatchell, 1994;Muhua et al, 1994;Clark and Meyer, 1994) and in two proteins, Num1p (Farkasovsky and Küntzel, 1995) and Karp9 (Miller and Rose, 1998), were found to result in defects in spindle positioning and orientation.…”

“…Elimination of other proteins, which are now known to be part of the dynactin complex, resulted in identical phenotypes. Deletion of either the actin-related protein Arp1 (Muhua et al, 1994;Clark and Meyer, 1994) or Jnm1p (McMillan and Tatchell, 1994) led to a failure to properly position and orient the mitotic spindle. As for dyn1⌬ mutants, astral microtubules are abundant and extend into the bud curving along the cortex (McMillan and Tatchell, 1994).…”