Experimental data and in silico analyses of sequenced bacterial genomes indicate that arginine repressor (ArgR) proteins and their respective target sites are surprisingly well conserved in very diverse bacteria. Arginine regulation therefore constitutes an interesting model system from the study of evolutionary aspects of bacterial regulation. Moreover, arginine repressor molecules are multifunctional, they repress the arginine biosynthetic genes and are involved in the activation of the various arginine catabolic pathways. Studies on the arginine repressor from the hyperthermophiles Thermotoga neapolitana and Thermotoga maritima have reinforced the uniform view of the bacterial ArgR–operator interaction, but have also revealed that the Thermotoga repressor exhibits unique features. Thus, its DNA-binding activity is nearly arginine-independent and exhibits poor sequence specificity. ArgRTn has a remarkable capacity to bind heterologous arginine operators and half-site targets.

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