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The PII family comprises a group of widely distributed signal transduction proteins. The archetypal function of PII is to regulate nitrogen metabolism in bacteria. As PII can sense a range of metabolic signals, it has been suggested that the number of metabolic pathways regulated by PII may be much greater than described in the literature. In order to provide experimental evidence for this hypothesis a PII protein affinity column was used to identify PII targets in A zospirillum brasilense. One of the PII partners identified was the biotin carboxyl carrier protein ( BCCP), a component of the acetyl- CoA carboxylase which catalyses the committed step in fatty acid biosynthesis. As BCCP had been previously identified as a PII target in A rabidopsis thaliana we hypothesized that the PII- BCCP interaction would be conserved throughout Bacteria. In vitro experiments using purified proteins confirmed that the PII- BCCP interaction is conserved in E scherichia coli. The BCCP- PII interaction required MgATP and was dissociated by increasing 2-oxoglutarate. The interaction was modestly affected by the post-translational uridylylation status of PII; however, it was completely dependent on the post-translational biotinylation of BCCP. [ABSTRACT FROM AUTHOR]