BIN2 phosphorylation of BES1 and BZR1 via a novel
mechanism. A, Phosphorylation of BES1 and BZR1 by BIN2 does not require
priming phosphorylation. CIP-treated GST-BES1 or GST-BZR1 was incubated
with GST-BIN2 or with a mutated GST-BIN2 fusion protein containing
Arg-80-Ala mutation, and assayed for protein phosphorylation as
described in the “Materials and Methods.” B, Both GST-BES1 and
GST-BZR1 proteins can be phosphorylated by an MBP-BIN2 fusion kinase.
C, FRATide has no inhibitory effect on the BIN2 phosphorylation of
either BES1 or BZR1. For all panels, the amount of protein used for the
kinase assays are indicated in the top strip, whereas the levels of
protein phosphorylation are shown in the bottom strip.