| Abstract: | The manner in which the fluF mutation was isolated makes it very interesting because it suggests that it may arise from an epigenetic defect. 5-Azacytidine (5-AC) treatment results in a high frequency of conversion of wild type to fluffy suggesting that the mutation may arise from the demethylation of a sequence that is normally methylated. If true, this would be the first example of an epigenetic event altering the development in a filamentous fungal system. It is also important to note that A. nidulans is characterized by a negligible level of methylation, if methylation exists at all (2). However, 5-AC has been shown to induce permanent heritable phenotypic changes in a variety of eukaryotic systems. Further evidence shows that control of gene expression in more complex systems is related to methylation of cytosines in the DNA and that these methylayion patterns are inherited (8). It would be interesting to characterize fluF and determine the mechanisms involved in its expression. Other chemical mutagens may be used to induce fluffy mutants as well. Although such treatment could result in many types of mutants, visual screening may be used to isolate only those mutants with the fluffy appearance. In these experiments two mutagens, 5-AC and 4-Nitroquinoline-1- (NQO), were used to induce and isolate fluffy mutants. 5-AC is an analog of cytosine that has a nitrogen atom substituted for a carbon at the site of methylation. When incorporated into the DNA, even at marginal levels, it inhibits eukaryotic DNA methyl transferase, thus causing extensive hypomethylation of the DNA. NQO is a classical mutagen that has been used extensively in A. nidulans because it induces mutation primarily in GC base pairs, and is easy to inactivate (3). In these studies, mutants were divided into two groups for the purpose of analyzing the 5-AC and NQO mutants separately. The fluffy strains were then divided into groups based on whether or not conidiation was completely abolished. Further characterization was based on appearance (fluffiness and conidiation), growth rate, reaction to changes in nutrient supply, and ability to extracellularly complement the acoD mutation. Genetic crosses were utilized to determine the number of loci affected and to obtain recombinants. |
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