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K Weber

Publications and source records attributed to K Weber.

At least 775 records · Page 43Linked to original sources
PubMed1972

Altered sequences changing the operator-binding properties of the Lac repressor: colinearity of the repressor protein with the i-gene map.

A technique is described for mapping point mutations in the first 59 amino-acid residues of the lac repressor from Escherichia coli, using less than 0.1 mumol (4 mg) of the purified protein. This technique was used to localize five mutations affecting the ability of the i-gene product to repress in vivo. These alterations are located at four different sites in the amino-terminal region of the repressor molecule. Three of these are missense mutations and result in changes from serine to proline (residue 16), threonine to alanine (residue 19), and alanine to valine (residue 53). Each amino-acid substitution alone is sufficient to eliminate repression in vivo, presumably by altering the operator binding activity. The remaining two independently-isolated mutations are identical, and result in a change from a glutamine codon at position 26 to an amber (UAG) codon. Since suppression of this nonsense mutation with amber suppressors that insert leucine, tyrosine, serine, or glutamine restores repressor activity to the molecule, glutamine(26) cannot be crucial for the operator-binding function. A comparison of the position of each altered residue with the genetic map enabled us to estimate the physical distance between several deletion-group endpoints.

Amino Acid Sequence↗
PubMed1972

Translational restarts: AUG reinitiation of a lac repressor fragment.

An early, spontaneous amber mutation in the lac i-gene allows translational reinitiation, which results in a mutant lac repressor. Comparison of the amino-terminal sequence of this mutant repressor with the partial amino-acid sequence of the wild-type lac repressor shows that reinitiation occurs at the first internal AUG codon, and results in a mutant protein lacking 42 residues at the amino-terminal end. This protein binds the inducer isopropyl-beta-D-thiogalactoside with normal affinity, and is capable of maintaining a tetrameric structure; however, it does not repress in vivo. These data suggest that the amino-terminal portion of the wild-type lac repressor is necessary either for direct binding to the lac operator or for the correct conformation for binding to DNA.

Adenine Nucleotides↗
PubMed1972

Bacteriophage Q replicase contains the protein biosynthesis elongation factors EF Tu and EF Ts.

The enzyme, Qbeta replicase, responsible for the replication of the RNA of Escherichia coli pahge Qbeta, is composed of four nonidentical subunits, three of which, I, III, and IV, are coded for by the bacterial genome, while subunit II is phage-specific. SUBUNIT IV IS SHOWN TO BE IDENTICAL TO THE PROTEIN SYNTHESIS ELONGATION FACTOR EF TS BY THE FOLLOWING CRITERIA: coelectrophoresis on polyacrylamide gels in sodium dodecyl sulfate and in urea buffers, identity of the first seven amino acids at the amino-terminus, precipitation of sub-unit IV by anti-EF T-factor serum, and stimulation of EF Tu-GDP exchange by subunit IV. Subunit III is shown to be identical to the protein synthesis elongation factor EF Tu by the following criteria: coelectrophoresis on sodium dodecyl sulfate gels, precipitation of EF Tu by anti-Qbeta replicase serum, binding of guanine nucleotides, and binding of phenylalanyl-tRNA. In addition, Qbeta replicase activity can be reconstituted from subunits I and II with EF Tu and EF Ts.

Acrylamides↗
PubMed1971

Localization of the zinc binding site of aspartate transcarbamoylase in the regulatory subunit.

Aspartate transcarbamoylase (EC 2.1.3.2) from Escherichia coli contains six zinc ions per molecule. Renaturation studies of this allosteric enzyme and its isolated subunits show that the metal binding site is in the regulatory polypeptide chain. Ultraviolet difference spectra of the cadmium and zinc derivatives have been used to show that the sites in the isolated subunit and the full enzyme are similar. Results with an apo derivative of the regulatory subunit suggest that the metal is not required for the binding of the feedback inhibitor, but that it is involved in the structural stability of the protein. A close relationship between the reactivity of the cysteine residues in the regulatory subunit and the metal ion has been found.

Aspartic Acid↗