Increased nuclear traffic chaos in hyphae of Aspergillus nidulans: molecular characterization of apsB and in vivo observation of nuclear behaviour

Filamentous fungi are model microorganisms for studying nuclear migration i n eukaryotic cells, Two genes, apsA and apsB (= anucleate primary sterigmat a), were identified in Aspergillus nidulans that affect nuclear distributio n in hyphae and specifically block conidiophore development at the metula s tage when mutant. Here we describe the cloning, sequencing and molecular an alysis of apsB, The gene encodes a 121 kDa coiled-coil, hydrophilic protein that was localized in the cytoplasm, No protein-protein interaction was de tected between ApsB and ApsA, a membrane-associated, previously identified protein. An apsB null mutant was characterized by Video epifluorescence mic roscopy using strains that express green fluorescent protein (GFP) in nucle i. With this novel approach, we have discovered a new mutant phenotype and have found that nuclei display an increased chaotic movement in older hypha l compartments that results in clustering and an uneven distribution of the se organelles, These results suggest a regulatory pole of ApsB in nuclear m igration.