Role of Specific Protein S-S Bonds in the Quasisubunit Structure of Chromosomal DNA

Effect of pancreatic lipase on supramolecular DNA complexes in eukaryotic cellsin vivo andin situ

“…This is apparently due to extraction of specific lipids/lipoproteins involved into stabilization of the conformation of supercoiled DNA during ethanol extraction, which confirms our previous data [9,10]. It should be noted that pronase P, RNase-A, and even phospholipase C have no marked effect on nucleoid of fixed cells.…”

“…Neutral lipids were identified in chromosomes [7,8], chromatin [6,13], nuclear matrix [4,10] and DNA [9,10].…”

“…It has been previously shown that supramolecular DNA complexes (DNA-SC) isolated from various eukaryotic cells by mild phenol extraction apart from RNA and non-histone protein (1-2%) contain 0.12-1.2% (depending on cell type) DNA-bound lipids (neutral lipids dominate over phospholipids), which can be extracted by the method of Folch only by treating these complexes with DNase I [9,10]. Various experimental approaches (sedimentation, rotation viscosimetry, electron microscopy, and light scattering) have demonstrated [5,10,11] the resistance of DNA-SC to proteolytic enzymes and their susceptibility for lipophilic agents (Triton X-100, deoxycholate, 35% ethanol)and phospholipases C, A, and D, which induced degradation of the complex into fragments with a molecular weight of about l0 s D.…”

Significance of specific protein S-S bonds in the structural-functional organization of DNA

“…A pH-dependent (at acid and neutral pH) thiol-mduced fragmentation of these DNA complexes to different-size subunits was established when the effects of various S-S splitting agents (ME, DTT, sodium borohydride, and glutathione reductase) were studied, this indicates the presence of several specific protein disulfide bonds in chromosomal DNA and their general biological significance [5,6,19] We think that thiol-induced fragmentation of SM DNA and PNM DNA results from the reducing influence of thiols on the RP S-S groups covalently bound to DNA and participating in the quasisubunit organization of DNA. As already reported {6], degradation of DNA complexes in the presence of thiols due to the presence of nucleases is unlikely.…”

“…Of particular importance in this context is the evidence that S-S bridges of RP covalently bound to DNA are involved in the tandem organization of the DNA subunits in the chromosome [14,15,17] and ha the attachment of the replicon loops to the nuclear matrix [3,16], i.e., in a higher level of DNA organization. This paper summarizes the results of our previous studies [5,6,9,19] on pH-dependent thiol-induced fragmentation of naturally occurring eukaryotic and prokaryotic DNA-RP complexes, on the determination of the size of thiol-induced DNA subunits and their secondary structure, and on the effects of thiols on the RP composition in these complexes. …”