Light and development regulate the expression of the albino-3 gene in Neurospora crassa

The albino-3 gene of Neurospora crassa codes for geranylgeranyl pyrophosphate synthase, an enzyme involved in the biosynthesis of carotenoids. The albino-3 locus encodes two overlapping transcription units that give rise to two mRNAs of 2.2 kb (al-3(c)) and 1>6 kb (al-3(m)), with the promoter of the latter residing in the transcribed region of the former. The 1.6-kb transcript was transiently expressed in the mycelium after light induction, while the 2.2-kb mRNA appeared in conidiating cultures only, independently of light. Al-3(c) mRNA was enhanced in the conidiophores and was impaired in mutants blocked at the early stages of conidiation; al-3(c) therefore represents a conidiation-specific transcript. The al-3(c) mRNA level increased upon illumination with blue light and fluctuated according to the circadian cycle.