What is a regulable promoter? And how does one regulate it?
Regulatable promoter means that the expression of the gene downstream of this promoter can be either induced or repressed. Met3 is an example of such regulatable promoters and it is regulated by the addition of methionine to the media. In yeast, Met3 gene encodes for ATP sulphurylase, an enzyme in the methionine biosynthetic pathway. Upon the addition of methionine, the gene driven by Met3 promoter is repressed, as its expression level is reversely correlated with the concentration of methionine added to the media (Figure from this paper):