| Here , we show that ARNT and Alt ARNT proteins are differentially phosphorylated by protein kinase CKII in vitro . ^^^ In contrast , DNA binding by an Alt ARNT / dioxin receptor heterodimer to the xenobiotic response element is not inhibited by phosphorylation with CKII , nor does Alt ARNT S77A behave differently from wild type Alt ARNT in the context of a dioxin receptor heterodimer . . ^^^ |