The Sl homothallic wild-type strain of Nectria haematococca produces grey-purplish colonies on PDA medium, due to synthesis of fusarubin and related naphthazarins. Seventeen yellow, beige or white mutants were isolated. On the basis of recombination tests they were divided into six distinct chromosomal regions. Four of them, designated befB, befC, belB and belC, may be regarded as regulatory genes which uncouple the processes of ageing and pigmentation that are normally associated in the wild-type. The two others, alyA and yelJ-beiW, control the biosynthesis of naphthazarins. Mutations in alyA were found epistatic to yelJ and beiW mutations, indicating that the aZyA locus acts on an earlier biosynthetic step than the yelJ-bei W region. The latter was shown to comprise two closely linked genes, yielding yellow or beige colours when mutated. Analysis of polar mutations suggests that they form a single unit of transcription. One of these two genes probably controls a late oxidation step in naphthazarin biosynthesis.
443The production by the fungus Nectria haematococca of antibiotic pigments related to fusarubin can be increased by (i) culture conditions unfavourable for good growth, (ii) multiplication of two cytoplasmic factors of unknown molecular nature, and (iii) mutation of nuclear genes. Six nuclear genes involved in the regulation of naphthoquinone release have been characterized and mapped. Some have three allelic forms: the wild allele, one or several mutated alleles determining the hyperproduction of pigments, and one or several intragenic suppressors of the latter mutations. These genes also seem to be involved in developmental events, especially in sexual reproduction.
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