A gene required for nuclear migration in Neurospora crassa codes for a protein with cysteine-rich, LIM/RING-like...

The ro mutants of Neurospora crassa are defective in nuclear migration and hyphal morphogenesis. Several of the ro loci have recently been shown to encode components of the dynein/dynactin motor complex. Here we report on the cloning and characterization of the ro-2 gene which codes for a novel 80 kDa protein that has two Cys-rich motifs which resemble zinc-binding LIM or RING domains thought to mediate protein-protein interactions. RO2 also contains several potential binding sites for Src homology 3 (SH3) domains. The ro-2B20 allele has a frameshift mutation within one of the Cys-rich domains which eliminates the C-terminal half of the open reading frame (ORF). Disruption of the ro-2 locus by repeat-induced point (RIP) mutation gave rise to progeny which have a nuclear migration defect, but which are also blocked in conidiation. The ability to assemble cytoplasmic microtubules and actin is maintained in ro-2 mutants, although subapical actin patches are more prominent. Based on these observations, the RO2 gene product is proposed to play a role in mediating interactions between components of the dynein/dynactin motor complex or in linking this complex to the nucleus or cytoskeleton.