Induction of the lac promoter in the absence of DNA loops and the stoichiometry of induction.

In vivo induction of the Escherichia coli lactose operon as a function of inducer concentration generates a sigmoidal curve, indicating a non-linear response. Suggested explanations for this dependence include a 2:1 inducer-repressor stoichiometry of induction, which is the currently accepted view. It is, however, known for decades that, in vitro, operator binding as a function of inducer concentration is not sigmoidal. This discrepancy between in vivo and in vitro data has so far not been resolved. We demonstrate that the in vivo non-linearity of induction is due to cooperative repression of the wild-type lac operon through DNA loop formation. In the absence of DNA loops, in vivo induction curves are hyperbolic. In the light of this result, we re-address the question of functional molecular inducer-repressor stoichiometry in induction of the lac operon.

High local concentration: a fundamental strategy of life.

Local increase in concentration is a basic principle of transcriptional control. Closer inspection reveals that it is a major force governing all interactions within and between proteins and DNA. Local increase in concentration acts on all levels of organization of living matter. The structures and functions of two central molecules of life-the linear polymers DNA and protein-are particularly illuminating examples. Local increase in concentration leads to cooperative or competitive interactions between molecules. It is an important principle of life.

"Cold-sensitive" mutants of the Lac repressor.

Thirteen of more than 4,000 single-amino-acid-replacement mutants of the Lac repressor, generated by suppression of amber nonsense mutants, were characterized as having a cold-sensitive phenotype. However, when expressed as missense mutations, none of the replacements cause cold sensitivity, implicating the suppression mechanism as being responsible for this phenotype.

What is life? The paradigm of DNA and protein cooperation at high local concentrations.

Many chemical reactions need high concentrations of the molecules involved in order to work efficiently. It is usually impossible for the cell to achieve the necessary high concentrations of all relevant molecules in unconfined solutions but this becomes possible if the high concentration is restricted around a relevant molecule. High local concentrations of interacting molecules have been observed many times in many different biological systems. The examples of Lac and Lambda repressors of Escherichia coli are presented and discussed here as useful paradigms of mechanisms for achieving high local concentrations of interacting protein protomers.

Genetics after Auschwitz.

The fast growth and flourishing of science and technology in a vacuum of values was instrumental in organizing the various genocide programmes in Nazi Germany. This use of science and scientists for both ideological and practical goals has been overlooked by most observers including the scientists themselves. Some reasons for this are discussed herein.

[Remembrance and denial. A critical look into correspondence of Adolf Butenandt, MPG president 1960-1972]. / Erinnerung und Ausblendung. Ein kritischer Blick in den Briefwechsel Adolf Butenandts, MPG Präsident 1960-1972.

Adolf Butenandt was one of the great biochemists of the last century. He was also a most successful organiser of science. Which price did he have to pay to be a success in the Third Reich? He persistently avoided seeing or hearing the blatant injustice around him. Injustice he knew nothing about did not exist. So he became the perfect model for the postwar generation of German scientists. Is he still a model today?