The nuclear actin‐related protein Act3p/Arp4 influences yeast cell shape and bulk chromatin organization

ACT3/ARP4 is an essential gene, coding for the actin‐related protein Act3p/Arp4 of Saccharomyces cerevisiae located within the nucleus. Act3p/Arp4 is a stoichiometric component of the NuA4, INO80, and SWR1 chromatin modulating complexes, and recruits these complexes onto chromatin for their proper chromatin functions. Mutated Act3p/Arp4 leads to impairment of the functions of these complexes and affects transcription of specific genes. Our results revealed significant disorder in the cell size and shape of act3/arp4 mutant cells, when grown at permissive temperature. act3/arp4 mutants have also demonstrated an increase in their nuclear diameters, thus suggesting that Act3p/Arp4 is a key regulator in the maintenance of cellular shape and nuclear organization. Furthermore, the use of Chromatin Yeast Comet Assay (ChYCA) for assessment of single‐cell bulk chromatin organization in act3/arp4 mutant cells allowed us to detect an elevated sensitivity toward nuclease action, denoting differences in higher‐order chromatin structure of the mutants. J. Cell. Biochem. 104: 59–67, 2008. © 2007 Wiley‐Liss, Inc.