<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)