Gene order in the qa gene cluster of Neurospora crassa

Four different types of crosses have been used to establish the order of the four genes in the qa gene cluster of Neurospora crassa, which encode the following proteins involved in the inducible catabolism of quinic acid: a regulatory (activator) protein (qa-1), catabolic dehydroquinase (qa-2), quinate dehydrogenase (qa-3), and dehydroshikimate dehydrase (qa-4). The four crosses involved (1) the ordering of the four qa genes relative to the closely-linked me-7 locus; (2) the ordering of the three other qa genes relative to a qa-1S mutant; (3) the use of a three factor cross--qa-3 X qa-4 qa-2 and (4) the use of four factor crosses--qa-1S X qa-3 qa-4 qa-2. The results of all four types of crosses agree in establishing an apparently definitive proximal to distal order, within the right arm of linkage group VII, i.e., qa-1 qa-3 qa-4 qa-2 me-7. The significance of a definitive establishment of the gene order within the qa cluster for an understanding of the organization and mechanism of genetic regulation in this cluster is discussed.