Accumulat ion of Microf i laments in a Colonial Mutant of Neurospora crassa

A morphological mutant of Neurospora erassa, snowflake, is shown to contain filaments which are about 70 A in diameter, and up to several microns long, and which usually bunch in groups of a few to several hundred. They may be found longitudinally or transversely arranged with respect o the long axis of the cell and, in many cases, they run up to the plasma membrane, but not through it. The filaments often are arranged in crystalline arrays but may also be found as separate filaments. Sometimes the filaments are closely appressed to nuclei and may be found inside them. It is likely that the filaments are not the result of the dissociation of microtubules and are most likely microfilaments like those found in other organisms. Their relationship to the origin of certain morphological mutants in Neurospora is discussed. Cytoplasmic filaments ranging in size from 40-120 A in diameter and up to several microns long have been described in many organisms. It has been suggested that filaments in the smaller size range (50-70,~), generally referred to as microfilaments, are actinlike and involved in contractile processes