Presence of particular transcription regulatory elements in the 5'-intergenic region shared by the chicken H2A-III and H2B-V pair

Abstract

The two chicken histone gene families, H2A and H2B, contain nine and eight members, respectively, within two major histone gene clusters. Six genes each from families H2A and H2B have been found to be closely associated in inverted directions as H2A/H2B gene pairs. Two previously sequenced H2A members ( H2A-I and H2A-II) encode the same amino acid (aa) sequence (class I), whereas seven sequenced H2B genes encode three different variants (classes I, II and III). In this study, we first sequenced H2A-III, a member of the H2A family, which is located in inverted orientation and 350 bp upstream from H2B-V, encoding the class-III H2B protein. The protein encoded by H2A-III differs from the class-I H2A protein in a single aa (Ala 70 → Pro; class II). As a step toward elucidation of the transcriptional regulation of the H2A and H2B families, we fused this 5'-intergenic region to the cat gene in inverted orientations to generate two chimeric plasmids, pH2A-III-350 and pH2B-V-350. Transient CAT assays using these constructs indicated that the promoter of H2B-V is more active than that of H2A-III. CAT assays with 5'-deletion mutants of H2A-III and H2B-V showed that they each possess particular transcriptional motifs which are located relatively close to, or apart from, their own coding regions. These findings, together with those reported previously on the H2A-V/H2B-II pair, suggest distinct manners of transcription regulation of different members of the chicken histone gene families, H2A and H2B.