Waga S, Mizuno S, Yoshida M
Department of Agricultural Chemistry, Tohoku University, Sendai, Japan.
Biochim Biophys Acta. 1989 Mar 1;1007(2):209-14. doi: 10.1016/0167-4781(89)90041-9.
The effect of nonhistone protein HMG1 and HMG2 from pig thymus on the in vitro nucleosome assembly has been examined with plasmid pSV2-gpt DNA and pig thymus core histones in the presence of DNA topoisomerase I. In the absence of core histones, the direct binding of HMG proteins could induce negative superhelical turns in DNA at low ionic strength, but not at physiological ionic strength. The nucleosome formation in the higher histone-to-DNA ratios at physiological ionic strength was not facilitated by HMG proteins, in contrast to poly(L-glutamic acid). HMG proteins suppressed the nucleosome assembly in the moderate histone-to-DNA ratios, resulting in the reduction of fully supercoiled DNA topoisomers. The suppression by HMG proteins was not cancelled by poly(L-glutamic acid). These suggest that the highly acidic carboxy terminal of HMG proteins does not act as an assembly factor, and that the HMG proteins, on the contrary, suppress the nucleosome formation, probably by binding to DNA in a way to inhibit the assembly into core particles.
利用质粒pSV2 - gpt DNA和猪胸腺核心组蛋白，在DNA拓扑异构酶I存在的情况下，研究了猪胸腺非组蛋白HMG1和HMG2对体外核小体组装的影响。在没有核心组蛋白的情况下，HMG蛋白的直接结合在低离子强度下可诱导DNA产生负超螺旋，但在生理离子强度下则不能。与聚（L - 谷氨酸）相反，在生理离子强度下较高组蛋白与DNA比例时，HMG蛋白并不能促进核小体形成。HMG蛋白在中等组蛋白与DNA比例时抑制核小体组装，导致完全超螺旋DNA拓扑异构体减少。聚（L - 谷氨酸）不能消除HMG蛋白的抑制作用。这些结果表明，HMG蛋白高度酸性的羧基末端并非组装因子，相反，HMG蛋白可能通过以抑制组装成核心颗粒的方式与DNA结合，从而抑制核小体形成。
