The following uncharacterized proteins have been shown [1] to share regions of similarities:

• Escherichia coli hypothetical protein yhdG and HI0979, the corresponding Haemophilus influenzae protein.
• Escherichia coli hypothetical protein yjbN and HI0634, the corresponding Haemophilus influenzae protein.
• Escherichia coli hypothetical protein yohI and HI0270, the corresponding Haemophilus influenzae protein.
• Bacillus subtilis hypothetical protein yacF.
• Rhodobacter capsulatus protein nifR3 and related proteins in Azospirillum brasilense and Rhizobium leguminosarum.
• Synechocystis strain PCC 6803 hypothetical protein slr0644.
• Synechocystis strain PCC 6803 hypothetical protein sll0926.
• Caenorhabditis elegans hypothetical protein C45G9.2.
• Yeast protein SMM1.
• Yeast hypothetical protein YLR401c.
• Yeast hypothetical protein YLR405w.
• Yeast hypothetical protein YML080w.

Although it has been proposed [2] that Rhodobacter capsulatus nifR3 is a transcriptional regulatory protein, we believe that these proteins constitute a family of enzymes whose active site could include a conserved cysteine which we have used as the central part of a signature pattern.