A family of bacterial proteins has been described [1] which groups transcriptional repressors, sugar kinases and yet uncharacterized open reading frames. This family, known as ROK (Repressor, ORF, Kinase) currently consist of:

• Xylose operon repressor (gene xylR) in Bacillus subtilis, Lactobacillus pentosus and Staphylococcus xylosus.
• N-acetylglucosamine repressor (gene nagC) from Escherichia coli.
• Glucokinase (EC 2.7.1.2) (gene glk) from Streptomyces coelicolor.
• Fructokinase (EC 2.7.1.4) (gene scrK or frk) from Pediococcus pentosaceus, Streptococcus mutans and Zymomonas mobilis.
• Escherichia coli allokinase (EC 2.7.1.55) (gene alsK).
• Escherichia protein mlc.
• Hypothetical Escherichia coli protein yajF and HI0182, the corresponding Haemophilus influenzae protein.
• Hypothetical Escherichia coli protein yhcI and HI0144, the corresponding Haemophilus influenzae protein.
• A hypothetical protein in nagH 5'region from Clostridium perfringens.

The repressor proteins (xylR and nagC) from this family possess a N-terminal region not present in the sugar kinases and which contains an helix-turn-helix DNA-binding motif. The domain common to all these proteins consists of about 300 residues. It is not highly conserved, but we could define a pattern centered on a glycine-rich region in the central part of the domain.