PubMed Health⌕ Search

Biomedical subjects

M Lederman

Publications and source records attributed to M Lederman.

At least 73 records · Page 4Linked to original sources
PubMed1969

DNA-directed peptide synthesis. VI. Regulating the expression of the lac operon in a cell-free system.

The operon model was proposed by Jacob and Monod in 1961 to explain the regulation of enzyme synthesis in bacteria. The model requires two genetic elements: a locus i which directs the synthesis of a repressor, and a locus called the operon which contains an operator gene and associated structural genes. The repressor is believed to stop RNA and enzyme synthesis by combining with the operator site. The inhibiting effect of the repressor is reversed by an inducer which interacts directly with the repressor. A DNA-dependent cell-free system has been developed for studying the regulation of the operon containing the gene for beta-galactosidase enzyme. In this cell-free system, gene activity is indirectly measured by the synthesis of part of the enzyme. Qualitatively, the regulation of the operon in the cell-free system is similar to its regulation in intact cells. The cell-free system is used to advantage in experiments where it is desirable to use predetermined levels of repressor, operon, and inducer. Such quantitative studies suggest that two inducer molecules are most effective in removing the repressor from the gene.

Cell-Free System↗
PubMed1967

Microbiology of saturated salt solutions and other harsh environments. II. Ribonucleotide dependency in the growth of a salt-habituated Penicillium notatum in salt-free nutrient media.

A strain of Penicillium notatum has been found growing upon media containing saturated calcium acetate which upon passage through media containing saturated KC1 loses its ability to grow at normal rates in salt-free glucose-peptone medium. This salt-habituated form can be restored to a near-normal growth rate by adding yeast extract, RNA or RNA-hydrolysates, but not by DNA or its hydrolysate. The 4 RNA nucleotides in combination replace yeast extract whereas riboside and base combinations do not. Adenylic, guanylic or cytidilic acids, singly or in various combinations, are even more effective, but uridylic acid alone is not active at all. Ribonucleotide pairs including uridylic acid are less active, but 3 ribonucleotide combinations are highly effective, even in the presence of uridylic acid. Differential effects were evident in mycelial form and sporulation, as well as growth. In addition to a direct role in Penicillium RNA metabolism, the significance of ribonucleotides in energy metabolism or cell wall synthesis is mentioned as alternatives to explain their restorative effects.

Culture Media↗