- Lysines 72, 80 and 213 and aspartic acid 210 of the Lactococcus lactis LacR repressor are involved in the response to the inducer tagatose-6-phosphate leading to induction of lac operon expression. van Rooijen, R.J., Dechering, K.J., Niek, C., Wilmink, J., de Vos, W.M. Protein Eng. (1993)