A comparative study of DNA-induced transformants and spontaneous revertants of inositolless Neurospora crassa

Inositolless (inl-) Neurospora crassa strains were treated with DNA (allo-DNA) of wild type N. Crassa. Hyphal fragments of a mycelial suspension of the N. Crassa ragged inl- strain used as recipient in our transformation experiments were found to consist of units containing 100--1000 nuclei. In this strain the inositol-independent (inl+) nuclei appearing after DNA treatment or by spontaneous reversion are present in the cytoplasm together with a large number of inl- nuclei. Thus, both transformation and reversion initially must result in heterokaryosis. Under appropriate conditions the inl- nuclei can be detected in the transformed and spontaneous inl+ phenotype revertant strains. Spontaneous revertants are usually characterized by the loss of their inl+ nuclei after transfers on inositol-supplemented medium. On minimal medium, the growth rate of transformed strains is significantly lower than that of spontaneous revertants. The inl+ gene appearing after DNA treatment or by spontaneous reversion is inherited as a trait bound to chromosomes. In crosses with the transformed strains, there is a significant increase in the number of non-Mendelian (6:2 and 5:3) tetrads in the inl locus.