<p> Nitrite is an intermediate in the pathway of nitrate assimilation. Several questions about reduction beyond the level of nitrite remain to be answered. </p> <p> The purpose of this investigation was to induce mutants deficient in nitrite reduction and to characterize these mutants phenotypically and genetically in an attempt to answer the following questions: </p> <p> (a) How many enzymes are required in vivo for nitrite reduction? </p> <p> (b) How many genes control nitrite reduction? </p> <p> (c) Is nitrite reductase localized within a particle? </p> <p> The results of this investigation showed that nitrite reductase is controlled by at least three genes and three cistrons on two linkage groups. None of the 'nitrite-mutants' were allelic with nitrate reductase mutants. There appeared to be more than one type of nitrite reductase activity in extracts of repressed wild type mycelia. Only one of these nitrite reductase species seemed to be necessary for the reduction of nitrite in vivo. </p> / Thesis / Master of Science (MSc)

<p> It was known, prior to this study, that there is a factor, or factors, in the centromere-proximal region of Neurospora sitophila which affect recombination near the centromere whether it is in Neurospora sitophila or transferred to Neurospora crassa. A location of this factor, or factors, was performed using tetrad and prototroph analysis. Further mapping of linkage group I of Neurospora crassa was undertaken when the Neurospora sitophila centromere-proximal region was present.</p> / Thesis / Master of Science (MSc)

<p> The investigation was carried out in order to determine the nature of some aberrant asci obtained, at a high frequency, from a single cross in Neurospora crassa. The subsequent investigations shed light on an aspect of pyridoxine metabolism and the nature of its genetic control, as well as showing the existence of dicentric chromosome and its great instability when present in the disomic condition. </p> / Thesis / Master of Science (MSc)

<p> Evidence of gene conversion and inter=allelic complementation from earlier work on the pdx-1 locus of Neurospora crassa suggested that a more detailed analysis of this locus should lead to a better understanding of these genetic phenomenao The work described in this thesis is concerned with the derivation of complementation maps for seven alleles of the pdx-1 locus, and with a study of recombination between these alleles through the isolation of prototrophs from suitably marked inter-allelic crosses together with the isolation of asci including those exhibiting the phenomenon of gene conversione In additioni the relationships betwean the pdx-1 alleles and a gene, en-pdx-1, affecting the excretion of a pigment into the medium on which the pdx-1 strains were grown were studied. The effect of desoxypyridoxine hydrochloride 9 and the extent to which the pdx-1 mutants respond to various normal forms of the vitamin, were also studied. </p> / Thesis / Doctor of Philosophy (PhD)

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