The ABC proteins of the YHBG family are related to those of the HAA family. The genes encoding these polypeptides are very often located 5' to the ntrA gene encoding sigma factor 54, involved in nitrogen regulation and diverse physiological functions in bacteria. These ABC are associated with a putative secreted protein (SS) and with an enzyme which has been shown to be a 3-Deoxy-D-manno-octulosonate 8-Phosphate Phosphatase. Indirect evidence suggests that yhgG is probably an essential gene for R. meliloti whose transcription is not linked to that of ntrA ( Pubmed : 2703463 ) and more recently ( Pubmed : 15380559 ) for E.coli.