Cisacting Sequences that Modulate Transcription of Wheat Histone H3 and 3′ Processing of H3 Premature mRNA

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Abstract
Transcripts of the 5′ and 3′ deletion mutants of the wheat (Triticum aestivum) histone H3 gene (pTH012) were studied with transformed sunflower (Helianthus annuus) cells into which they had been introduced via a Agrobacterium-based Ti-plasmid vector. An S1 nuclease assay of the steady-state levels of the H3 transcript showed that as 5′ deletion proceeded the level of transcript gradually decreased. This indicates that multiple cis-acting control elements exist in the 5′ flanking region of this gene. Removal of the characteristic hexameric sequence ACGTCA, the recognition site of the DNA-binding protein(s) HBP-1 (Mikami et al. 1987), resulted in a marked decrease in transcription efficiency. We concluded that this sequence is probably a cis-acting element that functions in the transcription of the H3 gene. SI analyses of transcripts from the 3′ deletion mutants of the H3 gene demonstrated the presence of signal sequences that act in the determination of the authentic 3′ end of H3 mRNA. Sequence comparisons in the 3′ flanking regions between the H3 gene and other plant histone genes indicated that the conserved sequence, TTT(N)13–16GATT, is present near the site at which the 3′ end of H3 mRNA was mapped. The possibility that this conserved sequence is a putative signal for the 3′ end formation of plant histone mRNA is discussed.

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