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H C Nelson

Publications and source records attributed to H C Nelson.

7 recordsLinked to original sources
PubMed1992

Trimerization of the heat shock transcription factor by a triple-stranded alpha-helical coiled-coil.

We have isolated and characterized a 91 amino acid fragment of the heat shock transcription factor from both Saccharomyces cerevisiae and Kluyveromyces lactis. The two protein fragments behave similarly: they form homotrimers, as indicated by sedimentation equilibrium and cross-linking, and contain approximately 80% alpha-helix, as indicated by circular dichroism. Sedimentation velocity and diffusion coefficients indicate that they have an elongated, nonspherical shape. We conclude the following: these fragments contain a domain which forms a trimer via a triple-stranded alpha-helical coiled-coil, similar to that found in influenza hemagglutinin.

Amino Acid Sequence↗
PubMed1989

Trimerization of a yeast transcriptional activator via a coiled-coil motif.

The transcriptional induction of heat shock genes is mediated by the heat shock transcription factor (HSF). We have investigated the oligomerization state of HSF from S. cerevisiae and find that it forms a trimer in solution and when bound to DNA. Trimerization is mediated by a region of HSF that, like the leucine zipper, is characterized by the occurrence of hydrophobic amino acids every 7 residues. We propose that it forms a three-stranded coiled coil.

Amino Acid Sequence↗
PubMed1986

Interaction of mutant lambda repressors with operator and non-operator DNA.

We have described a set of mutations that alter side-chains on the operator binding surface of lambda repressor. In this paper, we study the interactions of 12 purified mutant repressors with operator and non-operator DNA. The mutant proteins have operator affinities that are reduced from tenfold to greater than 10,000-fold compared to wild-type. Nine of the mutants have affinities for non-operator DNA that are similar to wild-type, two mutants show decreased non-specific binding, and one mutant has increased affinity for non-operator DNA. We discuss these findings in terms of the structural and energetic contributions of side-chain--DNA interactions, and show that certain contacts between the repressor and the operator backbone contribute both energy and specificity to the interaction.

Amino Acid Sequence↗
PubMed1985

Increasing and decreasing protein stability: effects of revertant substitutions on the thermal denaturation of phage lambda repressor.

The thermal denaturations of five revertant lambda repressors containing single amino acid substitutions in their N-terminal domains have been studied by differential scanning calorimetry. Two substitutions slightly decrease stability, and the remaining three render the protein more stable than wild type. The Gly48----Asn and Gly48----Ser proteins are 4 degrees C more stable than wild type. These two substitutions replace an alpha helical residue, and in each case a poor helix forming residue, glycine, is replaced by a residue with a higher helical propensity. We also present data showing that one revertant, Tyr22----Phe, has reduced operator DNA binding affinity despite its enhanced stability.

Amino Acid Sequence↗
PubMed1985

Lambda repressor mutations that increase the affinity and specificity of operator binding.

Intragenic, second-site reversion has been used to identify amino acid substitutions that increase the affinity and specificity of the binding of lambda repressor to its operator sites. Purified repressors bearing the second-site substitutions bind operator DNA from 3 to 600 fold more strongly than wild type; these affinity changes result from both increased rates of operator association and decreased rates of operator dissociation. Three of the revertant substitutions occur in the alpha 2 and alpha 3 DNA binding helices of repressor and seem to increase affinity by introducing new salt-bridges or hydrogen bonds with the sugar-phosphate backbone of the operator site. The fourth substitution alters the alpha 5 dimerization helix of repressor and appears to increase operator affinity indirectly.

Amino Acid Sequence↗
PubMedDate not supplied

The structure of an oligo(dA).oligo(dT) tract and its biological implications.

Poly(dA).poly(dT) has unusual properties in that it cannot associate into nucleosomes and short, phased runs of it cause DNA bending. The crystal structure of a B-type DNA dodecamer containing a homopolymeric run of six A.T base pairs shows that this region possesses special structural features, including a system of bifurcated hydrogen bonds, which explains some of the properties of this simple homopolymer.

Base Composition↗