Analysis of interaction between transcription factors in the regulation of wheat histone gene expression

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To identify the components involved in the formation of the special complex on the type I element in the wheat histone H3 promoter, which is known to confer the S-phase specific transcription, we carried out West-western screening with phosphorylated HBP-1a (17) as a probe. Aa a result, a novel bZIP-type transcription factor, HALF-1, was isolated from wheat cDNA library. With GST-fusions and by gel shift analysis, HALF-1 and HBP-1a (17) were demonstrated to interact with each other through their ZIP domains. Northern analysis revealed that HALF-1 expressed highly in the late S to early G2 phases. Transient assay revealed that HALF-1 had a potential activation domain that contained an amino acid stretch conserved among several plant bZIP proteins. The DNA-binding specificity and the structural characteristics showed that HALF-1 belonged to the HBP-1a subfamily.Wheat nuclear extracts prepared from S phase cells contained some specific DNA-binding activity directing to the hexamer motif and to the octamer motif. The S-phase specific hexamer-binding activity had the character similar to that of the HBP-1a subfamily and was suggested to be regulated by phosphorylation.