Influence of nonhistone chromatin protein HMG-1 on the enzymatic digestion of purified DNA

Abstract

The effect of chicken erythrocyte High Mobility Group protein 1 (HMG-1) on the enzymatic hydrolysis of purified double-stranded and single-stranded bacteriophage lambda DNA was studied. HMG-1 was found to inhibit the digestion of single- and double-stranded DNA by S1 nuclease and DNase I, respectively. HMG-I increased the rate of hydrolysis of double-stranded DNA by micrococcal nuclease, particularly at low HMG-1/DNA ratios, and had little effect on the hydrolysis of single-stranded DNA by micrococcal nucleases, even at high HMG-1 DNA ratios. We also present a semi-quantitative estimate that HMG-1 and HMG-2 occur in chromatin from rapidly dividing, cultured rat hepatoma cells at about 8 times the level that they occur in adult rat liver chromatin.

The nonspecific DNA-binding and -bending proteins HMG1 and HMG2 promote the assembly of complex nucleoprotein structures.

“…The periodicity of circularization of different length DNA fragments in the presence of HMG1 as calculated by Fourier analysis was 10.6--10.7 bp per turn, which is comparable with measurements of 10.45-10.6 bp per turn helical repeat on linear DNA in vitro (Bellomy and Record 1990). This conclusion is consistent with several observations that HMG1 and HMG2 are not unwinding or destabilizing the DNA helix (Shastri et al 1982;Butler et al 1985;Kohlstaedt et al 1987), but is in contrast to other reports (Javaherian et al 1979;Yoshida 1987;Sheflin and Spaulding 1989). It is possible, however, that a change in twist exerted by a single protein on the DNA molecule may not be detected in this assay.…”

High mobility group protein 1 preferentially conserves torsion in negatively supercoiled DNA

“…Javaherian et al proposed that HMG 1 induces negative supercoils into nicked circular DNA by local separation of DNA strands, based on thermal denaturation data (Javaherian et al, 1979). However, the response to thermal denaturation has now been attributed to protein aggregation and/or to contaminating unwinding protein (Shastri, 1982;Marekov et al, 1986). Helix destabilization therefore does not appear to be a valid explanation for the action of HMG 1.…”

“…The mechanism by which HMG 1 was originally thought to produce negative supercoils in nicked circular DNA was by strand separation, which was suggested by an early thermal denaturation study (Javaherian et al, 1979). More recent thermal denaturation studies in which protein aggregation was monitored, however, do not support the theory that HMG 1 acts to destabilize the DNA duplex (Shastri et al, 1982;Marekov et al, 1984Marekov et al, , 1986Butler et al, 1985). In fact, the helix destabilizing activity in one HMG 1 preparation was shown to be due to the presence of a contaminating unwinding protein (UP 1) (Marekov et al, 1986).…”

The Structural and Possible Functional Alterations on DNA and Chromatin Resulting fromcis-Pt(NH3)2Cl2Modification

“…It has been suggested that the replacement of H I histone with HMG 1 and 2 on nucleosomes may be involved in unfolding the local higher-order structure and increasing the accessibility of functional chromatin [35] . In addition, other accounts indi- cate that HMG 1 binding to DNA [37] and HMG 1 and 2 binding in chromatin [38] increase the rate of M.N. digestion.…”