Localization of actin and characterization of its isoforms in the hyphae ofNeurospora crassa

The actin of Neurospora crassa wild type Strain St. Lawrence has been purified, characterized and localized. A fungal 43 kDa protein was isolated by affinity chromatography on DNase I-Sepharose. This protein was identified as actin on immunoblots when an anti-actin monoclonal antibody raised against chicken gizzards was used as a probe. After two-dimensional gel electrophoresis three actin isoforms were detected. The distribution of actin in hyphae was examined by FITC-phalloidin staining of formaldehyde fixed hyphae. F-actin was found to be mainly concentrated in the hyphal tips in which it formed a uniform cap. Apical actin could be involved in hyphal morphogenesis, organelle motility and maintenance of polarity.