Joint study on nature of histone variants by gene targeting

44个鸡组蛋白基因中有39个（6个H1、9个H2 A、8个H2 B、8个H3和8个H4）位于一个110 kb的主基因簇中，其他基因位于4个独立的区域中。通过对42个基因的序列分析，获得了6个H1变异体、3个H2 A变异体、4个H2 B变异体、2个H3变异体和1个H4蛋白的组蛋白氨基酸序列。对这些组蛋白基因缺失突变体的系统分析表明，H1、H2 A、H2 B、H3和H4等组蛋白基因家族都具有弥补自身一个或两个成员缺失或失活的内在能力; 2、所有组蛋白基因家族都具有弥补主基因簇中一个等位基因缺失的内在能力。 ...更多信息 而对细胞功能没有影响。3.在DT 40突变体中，其在簇的约57 kb片段中包括的21个基因中的每一个都缺少两个拷贝，其余组蛋白基因的表达增加，导致所有五种组蛋白亚型的总mRNA的恒定稳态水平，而生长速率和整体染色质结构没有变化。仅12个H1基因拷贝中的单个拷贝或独特的H1变体就足以使DT 40细胞增殖。5，特定的H2 B变体负或正参与编码蛋白质的特定基因的表达调节，所述蛋白质在缺乏编码其的特定H2 B基因的DT 40突变体中变化。6，除了在染色质组织中发挥重要作用外，每个H1变体都单独参与DT 40细胞中特定基因的转录调控。此外，H1变体通常应作为特定基因表达的正或负调节剂起作用。少

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, … More 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