Biochemical analysis of isoallelic series at the al- i locus of Neurospora crassa

Abstract

The neutral carotenoids of 3 phenotypically distinct albino-1 (al-i) strains, a wild type, 2 heterokaryons containing 2 al-r alleles and 1 heterokaryon containing al-z + al-2 markers were analyzed. All al-r strains and the al-r heterokaryons contained large amounts of phytoene and only traces of higher carotenoids such as ~-carotene and lycopene which are responsible for the phenotypic variation at this locus (from pure white to lemon yellow). The biochemical lesion for al-z mutants affects phytoene dehydrogenase and enzyme "leakiness" accounts for the gene polymorphism. There is no evidence for interallelic complementation at the al-I locus.

Chromosomal loci of Neurospora crassa

“…See, for example, reference 1042. Strains carrying alleles ALS-14, RES-6, 34508, and RES-25 contain large amounts of phytoene (99 to 100% of the total neutral carotenoids), suggesting a lesion that affects phytoene dehydrogenase (398,1039) (see Fig. 9).…”

“…Name widely used for al-i allele 34508 (IR); with strains carrying this allele only mature peripheral conidia and conidiophores become visibly pigmented. Pigment of al-I mutants is said to be pale yellow (1039), but orange has been observed in 34508 strains (PB).…”

“…ylo-2: yellow-2 Yellow carotenoids. In addition to strains with mutations at loci designated ylo, strains with some al-i alleles (especially ALS4 and RES-25) produce lemon-yellow carotenoids, although in reduced quantity (1039,1042,1071). age-3 mutants are also yellow.…”