Fig 6. ZTL models demonstrate the importance of the Kelch repeat-LOV and Kelch repeat-substrate interaction.

A) Under the traditional LOV-substrate interaction without a LOV-Kelch interaction, the substrate may be too distant for ubiquitylation by a bound E2 conjugating enzyme. B-C) When these interactions are present, the substrate is brought into proximity with the E2, allowing its ubiquitylation. This interaction may either occur B) intra-molecularly, by folding the LOV domain towards the Kelch repeat domain of the same ZTL protein, or C) inter-molecularly. In the case of the inter-molecular model, two ZTL proteins share two ZTL substrates, with the LOV of one ZTL protein and the Kelch repeat of another interacting with the same substrate and with one another.