The expression of the trpD, trpC and trpBA genes of Streptomyces coelicolor A3(2) is regulated by growth rate and growth phase but not by feedback repression

Transformation of tryptophan auxotrophs of Streptomyces coelicolor A3(2) an d subsequent analysis have allowed the identification of four tryptophan bi osynthetic genes. Subcloning, complementation of trp strains, nucleotide se quencing of 5.1 kb and 1.95 kb of DNA and subsequent homology comparisons i dentified the trpC, trpB and trpA genes and trpD gene respectively. The arr angement of genes in the trpCBA cluster is unusual in that trpC is separate d by a small open reading frame, trpX, from the potentially translationally coupled trpB and trpA genes, Sequence analysis of the trpD gene revealed t he presence of a large mRNA loop structure directly upstream of the trpD-co ding region. S1 nuclease mapping studies of trpCXBA have revealed two major potential transcription start points, one just upstream of the trpC gene a nd the other located upstream of the trpX gene, S1 nuclease mapping of the trpD region revealed four fragment end-points. Quantitative S1 nuclease pro tection assays and a promoterless catechol dioxygenase reporter gene have r evealed that the expression of all these genes is growth phase dependent an d growth rate dependent, expression being maximal during early exponential phase and dropping off sharply in late exponential phase. This growth phase -dependent and growth rate-dependent regulation is the first reported in st reptomycete primary metabolism.