Interaction of Non-histone Chromosomal Proteins HMG1 and HMG2 with DNA

Abstract

Interaction between non-histone protein HMGl or HMG2 and DNA has been studied by using thermal denaturation and circular dichroism (CD) spectroscopy. We have made the following observations.1. The binding of each of these two proteins to DNA stabilizes the latter, as shown by an increase in melting temperature of 20 "C (from 45 "C to about 65 "C).2. There are 6.0 amino acids/nucleotide in HMGl-bound DNA and 5.0 in HMGZbound DNA which suggests that each HMGl molecule would cover about 20 base pairs of DNA and each HMG2 molecule would cover about 25 base pairs.3. The a-helical content of these two non-histone proteins in the complexes, estimated from the CD value at 220 nm, is about one third to one half that of total proteins in calf thymus chromatin.4. DNA conformation is distorted only slightly by the binding of protein HMGl or HMG2. 5.Neither the melting nor the CD properties of HMGl . DNA or HMG2 . DNA complexes differ substantially whether they are prepared by NaC1-gradient dialysis in urea or by direct mixing of protein and DNA at 0.15 M NaC1, followed by dialysis against the same buffer i.e. 0.25 mM EDTA (pH 8.0).Most of the physical studies of chromatin have so far emphasized the interaction between histones and DNA. However, it is evident that the non-histone chromosomal proteins also play an important part in the structure and function of chromatin. Since these proteins are generally quite different from the histones (e. g. having lower isoelectric points) the interaction of non-histone proteins with DNA could be quite different. In view of the importance of possible non-histone protein-DNA interactions in chromatin this study was initiated to investigate the interaction with DNA of two purified DNA-binding nonhistone proteins, proteins H M G l and HMG2 from calf thymus chromatin. These two proteins are extracted from chromatin with 0.35 M NaCl, contain 24-26 % lysine and arginine residues and 29-31 % aspartic and glutamic residues [l, 21. They possess 40 -50 % a-helix structures which are sensitive to pH as well as urea concentration [3,4]. Shooter et al.[2] and Goodwin et al. [5] showed that proteins HMGl and HMG2 bound DNA in a similar manner through ionic bonding between the basic amino acid Abbreviation. CD, circular dichroism ; proteins HMG 1 and HMG2, high-mobility-group non-histone proteins 1 and 2.residues and the phosphates of the DNA. Although there is no direct evidence for the association of HMG proteins with DNA in chromatin, the high content of basic amino acids as in the histones suggests that they are likely to be nucleic-acid-bound. They do not appear to be bound to RNA since extensive digestion of chromatin with ribonuclease does not release HMG proteins from chromatin [6] (and our own unpublished observations).Interaction of non-histone proteins, HMG 1 and HMG2, with DNA has been studied using thermal denaturation and circular dichroism (CD) spectroscopy. The thermal denaturation method has been used successfully in the studies of structural properties of chromatin, such as thermal s...

Tau could protect DNA double helix structure

“…That is to say, although neuronal tau facilitated DNA folding, it could not change the double helix structure. Similar property was reported when some DNA-binding proteins, such as HMG1 and HMG2, were studied by Yu et al [25]. These two proteins had been demonstrated as DNA chaperones [29].…”

“…The findings presented here indicate that tau binds to DNA with an effect of stabilizing the double strands. Such interaction may not induce a further conformational change in DNA double stands, similar to the results obtained from HMG family proteins [25]. Furthermore, there is increasing evidence that free radical-induced oxidative damage may play a role in the pathogenesis of Alzheimer's disease.…”

“…DNA samples were incubated with the protein at desired temperatures (25,40,50,60,70, 80 and 90 jC) for 10 min, followed by measurements of the absorbance (260 nm) of the mixture. The data were analyzed by the Origin 5.0 application software and differential method.…”

“…Some eukaryotic DNA-binding proteins, such as HMG 1 and HMG 2 , have been shown to display similar properties. In those cases, addition of HMG1 or HMG2 could cause the T m of T7 DNA to shift to a higher temperature [24,25].…”

HMGB1 in health and disease

“…HMGB1 binds to DNA with structure-specificity, but not sequence-specificity (Yu et al, 1977). Recognition and alteration of DNA structure plays a significant role in regulating DNA-related processes.…”