A positive regulatory element is involved in the induction of the beta-galactosidase gene from Kluyveromyces lactis.

The regulation of the LAC4 gene encoding beta-galactosidase in the yeast Kluyveromyces lactis has been studied. The expression of cloned LAC4 gene present on autonomously replicating plasmids was normally regulated by lactose or galactose as inducers. The LAC4 transcription initiation sites were mapped on two plasmids, PTY75-LAC4 and pKL2. The sites were found to be dependent on the level of gene expression and on the plasmid used. Under induced conditions, the normal cluster of initiation sites was used on both plasmids, whereas under non-induced conditions LAC4 on pKL2 showed additional sites. Deletion mapping of the 5' regulatory region of the LAC4 gene revealed a DNA element required for induction, presumably for the binding of a positive regulator.