DNA-binding protein that represses the expression of many genes essential for supplying Lactococcus lactis with amino acids during growth in milk. Seem to act on the major components of the proteolytic system, including the cell wall proteinase (PrtP), the oligopeptide transport system (Opp) and at least four intracellular peptidases (PepO1, PepN, PepC, PepDA2). Seem to be regulated via the dipeptide content in branched-chain amino acids (BCAA; isoleucine, leucine or valine). The BCAA may act directly or indirectly through GTP. May be a GTP-binding protein that senses the intracellular GTP concentration as an indicator of nutritional limitations. At low GTP concentration it no longer binds GTP and stop to act as a transcriptional repressor (By similarity). Belongs to the CodY family.