This thumb domain is important for acetyl CoA carboxylase activity [3, 7]. Unbiotinylated AccB C-terminal domain dimerizes, and biotinylated AccB C-terminal domain is monomeric [5]. AccB appears to interact with the C terminus of the BirA biotin ligase [9]. The interaction of BirA with AccB BirA-BCCP binding may preclude BirA dimerization and therefore DNA binding and transcriptional repressor activity of BirA [10]. A crystal structure of the biotinyl domain is presented at 1.8 angstrom resolution [11]. An NMR structure of the C-terminal domain has also been determined [7, 12] and implications with respect to specificity of protein-protein interactions are discussed [12]. Structural characterization of biotin carboxyl carrier protein (BCCP) by circular dichroism indicates that the biotin moiety may be partly engulfed within the protein rather than fully exposed in solution []. Secondary structure predictions have been made [13]. Mutation of the MKM biotinylation sequence reveals substrate requirements; the position of the lysine is critical and the flanking methionines are not [14]. Production of a protein with a mutation of the biotinylated lysine residue partially complements the heat sensitivity of another accB mutant, probably due to formation of mutant heterodimers [3]. A fabE/accB mutation is shown to disrupt biotinylation [15]. E119K and E147K mutant proteins exhibit defects in biotinylation that are due to defects in interaction with BirA, the biotin ligase [16]. Mutation of residue G133, G143, or V146 causes structural disruption of the protein [16]. A linker region N-terminal to the biotinoyl domain is also essential for function (but not required for biotinylation) [17]. Mutations in accB or accC suppress the inviability of an htrB mutant at 42°, which is due to accumulation of excess phospholipids [18]. AccB has similarity to Streptomyces venezuelae ISP5230 JadJ protein, which is involved in biosynthesis of the polyketide antibiotic jadomycin B [19]. Pseudomonas aeruginosa AccB functionally complements conditional lethality of an accB mutation in E. coli [20]. AccB exhibits an abnormally large apparent molecular weight of 22.5 kDa, compared to the predicted molecular weight of about 16.7 kDa [15]. Purification of AccB is described [4]. AccB peptides have been fused to exogenous proteins for use as biotinylation signals that facilitate purification [21, 22]. Reviews: [23, 24]