Represses the expression of the murPQ operon involved in the uptake and degradation of N-acetylmuramic acid (MurNAc). Binds to two adjacent inverted repeats within the operator region. MurNAc 6-phosphate, the substrate of MurQ, is the specific inducer that weakens binding of MurR to the operator. Also represses its own transcription. Amino-sugar metabolism; N-acetylmuramate degradation [regulation]. Homotetramer. Repressed by itself and by the cAMP receptor protein crp. Cells lacking this gene show an abolition of the extensive lag phase observed when grown on MurNAc and a 20-fold enhancement of murQ transcription. Neither GlcNAc-6-P, GlcNAc, anhydroMurNAc, MurNAc, nor muramyl dipeptide have an effect on MurR binding to the operator site.