Interaction between the bHLH-PAS protein Trachealess and the POU-domain protein Drifter, specifies tracheal cell fates.

bHLH-PAS proteins represent a class of transcription factors involved in diverse biological activities. Previous experiments demonstrated that the PAS domain confers target specificity (Zelzer et al., 1997. Genes Dev. 11, 2079-2089). This suggested an association between the PAS domain and additional DNA-binding proteins, which is essential for the induction of specific target genes. A candidate for interaction with Trh is Drifter/Ventral veinless, a POU-domain protein. A dual requirement for Trh and Drifter was identified for the autoregulation of Trh and Drifter expression. Furthermore, ectopic expression of both Trh and Dfr (but not each one alone) triggered trh autoregulation in several embryonic tissues. A direct interaction between Drifter and Trh proteins, mediated by the PAS domain of Trh and the POU domain of Drifter, was demonstrated.