DNA sequence, organization and regulation of the qa gene cluster of Neurospora crassa

In Neurospora, five structural and two regulatory genes mediate the initial events in quinate/shikimate metabolism as a carbon source. These genes are clustered in an 18 x 10(3) base-pair region as a contiguous array. The qa genes are induced by quinic acid and are coordinately controlled at the transcriptional level by the positive and negative regulators, qa-1F and qa-1S, respectively. The DNA sequence of the entire qa gene cluster has been determined and transcripts for each gene have been mapped. The qa genes are transcribed in divergent pairs and two types of transcripts are associated with each gene: basal level transcripts that initiate mainly from upstream regions and are independent of qa regulatory gene control, and inducible transcripts that initiate downstream from basal transcripts and are dependent on qa-1F binding to a 16 base-pair sequence. We discuss how both types of transcription relate to the organization of the qa genes as a cluster and how this may impose constraints on gene dispersal.