The 3-A structure of DNA-binding protein II, which exhibits histone-like properties in bacteria, has been determined. The molecule is dimeric and appears to bind to the phosphate backbone of DNA through two symmetry-related arms. A mechanism by which the protein induces DNA supercoiling is proposed.

The intrinsic persistence length of carboxymethyl cellulose (CMC) is determined by size exclusion chromatography in combination with multiangle laser light scattering (SEC−MALLS) as well as from potentiometric titrations. Samples with degree of substitution (ds) ranging from 0.75 to 1.25 were investigated. The relation between molar mass M and radius of gyration R g as obtained by SEC−MALLS is determined in 0.02, 0.1, and 0.2 mol L-1 NaNO3. Using the electrostatic wormlike chain theory a bare (intrinsic) persistence length L p0 of CMC is assessed at 16 nm, irrespective of the degree of substitution. A somewhat lower value (12 nm) is obtained when Odijk's theory for the description of polyelectrolyte dimensions is applied. The difference between L p0 assessed from both models is discussed briefly. Potentiometric titrations were carried out in NaCl solutions (ranging from 0.01 to 1 mol L-1). From the titrations the radius of the CMC backbone was obtained by application of the model of a uniformly charged cylinder. The radius amounts to 0.95 nm for CMC ds = 0.75, and increases to 1.15 nm for CMC with ds = 1.25. The pK for the intrinsic dissociation constant of the carboxyl groups (i.e., at zero degree of dissociation) amounted to 3.2. L p0 was also deduced from potentiometric titrations. A model developed by Katchalsky and Lifson, which relates the dissociation behavior of a polyelectrolyte to the stiffness of its chain, was applied to CMC. From analyses of the potentiometric titrations an intrinsic persistence length of 6 nm was deduced. The difference between L p0 assessed from SEC−MALLS and potentiometric titrations is discussed briefly.

DNA‐protein complexes formed in vitro with isolated DNA‐binding proteins from the thermoacidophilic archaebacterium Sulfolobus acidocaldarius were analyzed by electron microscopy. Two of the proteins (10a and 10b) formed specific structures after incubation with DNA. Protein 10a, at low protein concentrations, showed individual small spots on the DNA and at high concentrations evenly covered doublestranded DNA. Protein 10b showed three different types of regular structures: one with single‐stranded and two with double‐stranded DNA. Using double‐stranded DNA, 10b first bound cooperatively to two strands forming long, plait‐like structures only slightly shorter than respective free DNA. The complex consists of two right‐handed, interwound fibers, with a helical pitch of 26 nm and a diameter of ∼10‐11 nm. At higher protein concentration than needed to package all DNA into the complex with two double‐stranded DNAs, the two DNAs were separated again and a new structure was formed evenly covering only one DNA strand. Both structures showed no significant contraction of the length of the DNA covered in the complex. Nucleoprotein formed with single‐stranded ΦX174 DNA had a diameter of ∼11 nm and could form circles with a contour length of 0.5 μm.

The applied pH during the TEMPO-mediated (2,2,6,6-tetramethylpiperidine-1-oxyl) oxidation of the polysaccharide pullulan has a substantial influence on the molar mass distribution of the products. The least degradation was found in the pH range 9.2-9.7 and especially at higher pH, significant degradation occurs due to β-elimination. Four samples were prepared at pH 9.4 with different degrees of oxidation and the influence of the charge parameter ξ on the rms radius of gyration at various ionic strengths (Cs) was determined with size exclusion chromatography (SEC) using a multiangle laser light scattering (MALLS) detection system. Experimental values were compared to values obtained with the wormlike chain model for polyelectrolytes in combination with excluded-volume theory. The ionic strength-linear charge density dependence of the rms radius of gyration is quite accurately described, whereas the prediction of its absolute value is more problematic for lack of a quantitative description of solvent quality. However, very reasonable values for the rms radii of gyration are obtained using eq 15, originally derived as a scaling relation. Furthermore, it is shown that there is no discrepancy between the apparent persistence length, proportional to ξ/Cs 1/2 , and the real persistence length, proportional to ξ 2 /Cs, when excluded-volume effects are accounted for.

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