| Research Abstract |
Thirty-nine of the 44 chicken H1 and core histone genes are located in a major histone gene cluster of 110 kb. Using gene targeting techniques, we generated several DT40 mutants, respectively, which are devoid of one or two particular histone genes, one allele of the major gene cluster of 110 kb, an approximately 57 kb segment of the cluster carrying 21 genes, and 11 of the 12 H1 gene copies. In addition, we generated four DT40 mutants, respectively, devoid of chHDAC-1, 2, 3 and 4. Systematic analyses of the resultant mutants led us to some noticeable conclusions, as follows.
1) Histone gene families, H1, H2A, H2B, H3 and H4, have the inherent ability to compensate for the deletion of approximately half of their own constituents and to maintain the amount of each of the histone subtypes in stoichiometric balance, based on increases in the expression of the remaining members, regardless of the complete disruption of one allele of the major gene cluster or the disruption of approximately
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half segments of the two alleles. Therefore, one allele of the major histone gene cluster is enough for cell proliferation.
2) The deletion of 11 of the 12 H1 gene copies resulted in insignificant influence on the cell functions, i.e. the growth rate and global chromatin structure, indicating that only one copy of the H1 genes is enough for cell proliferation.
3) The protein patterns on 2D-PAGE are not altered in the case of the deletion of one allele of the cluster, due to no changes in the composition of any histone variant, but vary in the case of the deletion of approximately half segments of the cluster, and the latter plus more H1 gene(s), due to changes in the quality of the H1 and core variants.
4) The protein patterns are altered in the mutants, respectively, lacking particular H1 and H2B variants. The variable proteins are specific for the corresponding mutants, suggesting that the H1 and core variants should play individual roles in regulation of the expression of specific genes, probably through alterations in the chromatin structure localized in specific genomic regions.
5) chHDAC-2 controls the amount of the IgM H-chain at the steps of both transcription of its gene and the alternative processing of its pre-mRNA.
6) chHDAC-3 is essential for the viability of DT40 cells. Less
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