I. Imidazole compounds accumulated by purine mutants of Neurospora crassa. II. Complementation studies with isoleucine-valine mutants of Neurospora crassa

• Main Author: Bernstein, Harris
• Format: Others
• Published: 1961
• Online Access: https://thesis.library.caltech.edu/978/1/Bernstein_h_1961.pdf; Bernstein, Harris (1961) I. Imidazole compounds accumulated by purine mutants of Neurospora crassa. II. Complementation studies with isoleucine-valine mutants of Neurospora crassa. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/S02K-EV24. https://resolver.caltech.edu/CaltechETD:etd-03172006-084834 <https://resolver.caltech.edu/CaltechETD:etd-03172006-084834>

PART I: Imidazole Compounds Accumulated by Purine Mutants of Neurospora crassa: The mycelis of mutants defective at seven adenine loci were investigated for imidazole accumulation. By the use of a paper chromatographic technique five imidazoles not present in wild type were discovered in the mutants. Two of these were isolated and characterized as the ribotide and riboside of 5-amino-4-imidazole-N-succinocarboxamide. The third compound was identified as 5-aminoimidazole riboside, and the fourth as 5-amino-4-imidazolecarboxamide riboside. The distribution of these accumulated compounds among the mutants allowed a correlation between the adenine loci and the steps of purine biosynthesis. Part II: Complementation Studies with Isoleucine-Valine Mutants of Neurospora crassa: A total of 616 mutants capable of growth on a medium supplented with isoleucine and valine, but not on minimal medium, were obtained through the use of 9 different mutagens. On the basis of heterokaryon complementation tests all of the mutants could be allocated to five groups. These groups were designated val-1, val-2, iv-1, iv-2, and iv-3. Mutants in the val-1 and val-2 groups required valine as the sole supplement. Members of the iv-1 group were probably blocked in the dehydrase step of isoleucine-valine biosynthesis, and were characterized by slow growth between 4 and 6 days after inoculation on minimal medium. Evidence was also presented to indicate that iv-3 mutants were blocked in the condensing step of isoleucine-valine biosynthesis. An extensive program of complementation testing was performed among mutants within both the iv-2 and the iv-3 groups. The results of these tests allowed, in each case, the formulation of complementation map. However, three iv-3 mutants were found which could not be reconciled with any linear pattern. An interesting feature of the iv-3 studies, and to some extent of the iv-2 studies, was the finding that among the mutants found the same patterns of complementation interaction often reoccured. Mutants with the same complementation behavior constitute a complementation subgroup. Each of these subgroups usually contained mutants representative of several different mutagenic treatments. The hypothesis was considered that this observed clustering reflects an intrinsic property of the genetic locus --- namely that each locus has associated with it a unique pattern of discrete complementation subgroups. It was hoped that these genetc regularities would prove, in the course of further biochemical investigations, to relate in a direct way to the structural properties of the enzyme molecule.