<p>A) L-Subunit B showing (+)-ABA (in yellow) bound to a surface cleft adjacent to Y100. While distal from the RuBP (in green) binding site (~ 30 Å away), this site is in closer proximity to the positively charged regulatory latch region comprised of residues R41, R134, K305, H310, R312 and involves residues that immediately precede and follow the 90–97 loop region implicated in binding to Rubisco activase. B) The omit F<sub>o</sub>-F<sub>c</sub> electron density maps represented by the green hatching at ~ 2 sigma, were calculated without ABA included in the model. (+)-ABA (in yellow with red oxygens) is shown, bound to the A L-subunit. The terminal carboxylate is shown anchored to R139; the ketone forms a short H-bond with Y85; and the hydroxyl group at the chiral center forms a H-bond with K356. The hydroxyl group also has a weak 3.3 Å interaction with a water that is part of an H-bond and ionic matrix involving the side chains of Y100, E88, R358 and Y363.</p
