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Actin has a pivotal function in hyphal morphogenesis in filamentous fungi, but it is not certain whether its function is equivalent to that of a morphogen, or if it is simply part of a mechanism that executes orders given by another regulatory entity. To address this question we selected for cytochalasin A resistance and isolated act1, the first actin mutant in Neurospora crassa. This mutant branches apically and shows an altered distribution of actin at the tip. Based on the properties of this mutant, we propose a model of tip growth and branching in which actin effects tip growth by regulating the rate of vesicle flow from proximal to distal regions of a hypha, thereby controlling the tip-high gradient of cytoplasmic calcium. The actin-controlled calcium gradient at the tip is necessary for maintenance of tip growth as well as the dominance of one polarized site at the hyphal tip. The phenotype of act1 indicates that actin controls the balance between lateral and apical branching. [Copyright &y& Elsevier]

Reports on the presence of plasmid suppressors in natural populations of the fungi Neurospora intermedia. Testcrosses of progeny of cross 1940; Dependence of plasmid suppression on a strain-specific interaction; Segregation of original full suppression of all plasmids; Interaction type of suppression in ascogenous tissue in one sexual cycle.

Reports two cases of paternal transmission of genetic elements of organelles in crosses of the fungus Neuspora. General rule in anisogamous matings; Linear plasmids; Mitochondrial deoxyribonucleic acid (DNA); Heteroplasmons; Mitochondrial segregation and assortment; Associations between genomic compartments and between genomic and extragenomic elements.