Raphael Kram

The pleiotypic response in mammalian cells: Search for an intracellular mediator

Abstract The reactions included in the definition of this regulatory program, called the “pleiotypic response”, are very similar to those under “stringent” control in bacteria. The latter appears to be mediated by a novel nucleotide, ppGpp, and we therefore assayed for the presence of this nucleotide in cultured fibroblasts under a variety of conditions of growth restriction which elicit the pleiotypic response. We were unable to detect it in any of these circumstances and we conclude that ppGpp is not the mediator of the pleiotypic response, at least in the cell lines studied.

Studies on amino acid control of cellular function

Abstract Amino acid starvation of 3T3 and SV3T3 cells leads to inhibition of precursor uptake and incorporation into macromolecules, whereas protein degradation is not affected. In both cell types, intracellular cAMP concentrations decrease slightly after 18 hr of amino acid deprivation. In contrast, serum starvation, which also decreases precursor uptake, does so primarily in untransformed cells, by a mechanism involving an increase in cAMP levels.