Joint study on nature of histone variants by gene targeting

44个鸡组蛋白基因中的39个（6个H1, 9个H2A， 8个H2B， 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。对42个基因进行序列分析，得到组蛋白氨基酸序列为6个H1变异、3个H2A变异、4个H2B变异、2个H3变异和1个H4蛋白。为了阐明这些变异的新性质，我们利用基因靶向技术产生了许多不同类型的鸡DT40突变体，这些突变体缺乏适当的组蛋白基因。对这些组蛋白基因缺陷突变体的系统分析揭示了以下几个值得注意的结论。所有组蛋白基因家族H1， H2A,H2B，H3和H4都具有补偿其自身成分中一个或两个成员的缺失或失活的固有能力。所有组蛋白基因家族都具有补偿主要基因簇中一个等位基因的破坏的内在能力，而且对细胞功能没有影响。3、在DT40突变体中，大约57 kb片段中包含的21个基因各缺少两个拷贝，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保持恒定的稳态水平，而生长速度和整体染色质结构没有变化。仅12个H1基因拷贝的一个拷贝或一个独特的H1变异就足以使DT40细胞增殖。在缺乏特定H2B基因编码的DT40突变体中，特定H2B变异体负或正参与编码蛋白质的特定基因的表达调控。6、除了在染色质组织中发挥重要作用外，每种H1变异都单独参与DT40细胞中特定基因的转录调节。此外，H1变异通常应作为特定基因表达的阳性或阴性调节因子。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