Genetic evidence for a microtubule-destabilizing effect of conventional kinesin and analysis of its consequences for the control of nuclear distribution in Aspergillus nidulans

Conventional kinesin is a microtubule-dependent motor protein believed to b e involved in a variety of intracellular transport processes. In filamentou s fungi, conventional kinesin has been implicated in different processes, s uch as vesicle migration, polarized growth, nuclear distribution, mitochond rial movement and vacuole formation. To gain further insights into the func tions of this kinesin motor, we identified and characterized the convention al kinesin gene, kinA, of the established model organism Aspergillus nidula ns. Disruption of the gene leads to a reduced growth rate and a nuclear pos itioning defect, resulting in nuclear cluster formation. These clusters are mobile and display a dynamic behaviour. The mutant phenotypes are pronounc ed at 37 degreesC, but rescued at 25 degreesC. The hyphal growth rate at 25 degreesC was even higher than that of the wild type at the same temperatur e. In addition, kinesin-deficient strains were less sensitive to the microt ubule destabilizing drug benomyl, and disruption of conventional kinesin su ppressed the cold sensitivity of an alpha -tubulin mutation (tubA4). These results suggest that conventional kinesin of A. nidulans plays a role in cy loskeletal dynamics, by destabilizing microtubules. This new role of conven tional kinesin in microtubule stability could explain the various phenotype s observed in different fungi.