Presence of distinct transcriptional regulatory elements in the 5'-flanking region shared by the chicken H3 histone gene homopair

One allele of the major histone gene cluster is enough for cell proliferation of the DT40 chicken B cell line

Thirty-nine of the 44 chicken histone genes are located in a major histone gene cluster of 110 kb, the others residing in four separate regions. We generated a heterozygous chicken DT40 mutant, 1/2 delta110 kb, devoid of one allele of the cluster, using gene targeting techniques. Analyses of the mutant revealed that the growth rate of DT40 cells was unchanged even in the absence of one allele of the cluster. Moreover, analyses involving a RNase protection assay, SDS-PAGE or Triton-acid-urea-PAGE revealed not only that in the 1/2 delta110 kb mutant the steady-state levels of total mRNAs of gene families H1, H2A, H2B, H3 and H4 remained constant, but also that the amounts of histones H1, H2A, H2B, H3 and H4 were not changed. A comparison by 2D-PAGE revealed no changes in total cellular protein patterns of the mutant. These observations demonstrate that all the histone gene families have the inherent ability to compensate for the disruption of one allele of the gene cluster, with no influence on cell functions.

Possible involvement of a ubiquitous and several distinct elements in the transcription regulation of the chicken H3 histone gene family

We have studied possible modes of transcription regulation of four members (H3-II, H3-III, H3-IV and H3-V) of the twelve chicken H3 genes. Results of transient CAT assays using 5'-truncated mutants of H3-IV, together with those reported previously for H3-II and H3-III, indicated that all these four H3 genes possessed a ubiquitous element, the CCAAT sequence, in addition to several distinct elements. Transient CAT assays using the 5'-extended mutants of these four H3 genes showed that the promoter activities decreased with increasing lengths of the 5'-extended fragments, and that the effects were strong for H3-IV and H3-V, but only moderate for H3-II and H3-III.

Coordinate regulation of the human TAP1 and LMP2 genes from a shared bidirectional promoter

Recently, four genes (TAP1, TAP2, LMP2, LMP7) involved or potentially involved in the processing and transport of major histocompatibility complex class I-associated antigen to the endoplasmic reticulum have been identified. We now report the initial characterization of the bidirectional promoter for the human transporter associated with antigen processing 1 (TAP1) and low molecular mass polypeptide 2 (LMP2) genes. These genes are divergently transcribed from a central promoter region of only 593 bp. Functional analysis using a bidirectional reporter system demonstrates the minimal 593-bp promoter is sufficient for concurrent expression in both directions. There is no TATA box homology at either end but there is a prevalence of GC boxes. Transcription is initiated at multiple sites for each gene without any of the TAP1 transcripts overlapping with the LMP2 transcripts. The region proximal to the TAP1 gene is required for maximal basal level expression of not only TAP1 but also LMP2. Furthermore, this region is necessary for tumor necrosis factor alpha (TNF-alpha) induction of both genes. Site-specific mutations of an NF-kappa B element in the TAP1 proximal region blocked induction by TNF-alpha in both the TAP1 and LMP2 directions. An adjacent GC box was required for basal expression of both genes as well as augmenting the TNF-alpha induction of the distal LMP2 gene. In vivo genomic foot-printing of this region revealed strong protein/DNA interactions at the NF-kappa B and GC box consensus sequences. In vitro binding studies confirmed the capacity of the NF-kappa B site to bind p50/p65 and p52/p65 heterodimers and of the GC box to bind Sp1. Thus, the promoter elements proximal to the TAP1 gene play a significant role in regulating basal and induced expression of both TAP1 and LMP2. The findings presented in this report clearly link LMP2 expression with TAP1 expression and provide additional suggestive evidence linking LMP2 to class I antigen presentation.

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

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 (Ala70-->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.

The chicken histone gene family

1. Most of the chicken 43 core and H1 histone genes belong to two major histone gene clusters. 2. Each of six H1 genes encodes a different H1 protein sequence. 3. The known core histone genes, four H2A, seven H2B, and seven H3 genes, respectively, encode two, three and three different protein variants, whereas the four known H4 genes encode the same amino acid sequence. 4. The core histone genes have particular transcription regulatory elements within the 5'-flanking regions and the regulations of their expressions are distinct, even though they are members of the same core histone gene family. 5. There are some undefined differences in the DNA structures of the particular core histone genes in various chicken tissues and these structural variations probably result in differences in their transcriptional regulation.