Hex-Motif-Specific Binding Protein HBP-1b(c38) can Activate Transcription Without Interacting with a Target DNA Sequence.

Abstract

The type I element (CCACGTCACCAATCCGCG) is a cis-acting element essential for cell cycle-dependent expression of the wheat histone H3 gene (TH012). This element consists of two distinct motifs, Hex (CCACGTCA) and Oct (CGCGGATT). To understand the mechanism of transcriptional regulation via the type I element, we analyzed the function of HBP-1b (c38), a Hex-motif-specific DNA-binding protein of wheat, by using a transient expression system. Cotransfection experiments with effector and reporter plasmids indicated that overexpressed HBP-1b (c38) did not activate expression of the reporter gene with a normal type I element but unexpectedly enhanced the activity of the promoter with a mutated Hex-motif-containing type I element. This activation was Oct-motif-dependent. Basic, leucine zipper, and acidic regions of the HBP-1b (c38) protein were necessary for this activation. These results suggest that HBP-1b (c38) has an ability to activate transcription without interacting with a target DNA sequence.