|Budget Amount *help
¥6,700,000 (Direct Cost: ¥6,700,000)
Fiscal Year 1996: ¥3,300,000 (Direct Cost: ¥3,300,000)
Fiscal Year 1995: ¥3,400,000 (Direct Cost: ¥3,400,000)
Thirty-nine (six H1, nine H2A,eight H2B,eight H3 and eight H4) of the 44 chicken histone genes are located in a major gene cluster of 110 kb, the others residing in four separate regions. Results of sequence analyzes of the 42 genes generated a set of the histone amino acid sequences as follows : six H1 variants, three H2A variants, four H2B variants, two H3 variants and an H4 protein.
To clarify the new nature of these variants, we generated many different types of the chicken DT40 mutants, which are devoid of the appropriate histone genes, using gene targeting techniques. Systematic analyzes of these histone gene-deficient mutants revealed several noticeable conclusions, as follows.
1, All of histone gene families H1, H2A,H2B,H3 and H4 have the inherent abiliby to compensate for the deletion or inactivation of one or two members of their own constituents.
2, All the histone gene families have the inherent ability to compensate for the disruption of one allele of the major gene cluster,
with no influences on cell functions.
3, In the DT40 mutant, which lacks two copies each of the 21 genes included in the approximately 57 kb segment of the cluster, expression of the remaining histone genes increased, resulting in constant steady-state levels of total mRNAs of all the five histone subtypes, with no changes in the growth rate and global chromatin structure.
4, Only a single copy of the 12 H1 gene copies or a unique H1 variant is enough for proliferation of DT40 cells.
5, A particular H2B variant participates negatively or positively in regulation of expression of specific genes that encode the proteins that vary in the DT40 mutant devoid of a particular H2B gene encoding it.
6, Each of the H1 variants possesses individual participation in transcription regulation of specific genes in DT40 cells, in addition to a vital role in the chromatin organization. Furthermore, the H1 variants should generally function as either a positive of negative regulator of expression of particular genes. Less