Publications (5)16.78 Total impact
- [Show abstract] [Hide abstract] ABSTRACT: Ras proteins are small GTPases playing a pivotal role in cell proliferation and differentiation. Their activation depends on the competing action of GTPase activating proteins and guanine nucleotide exchange factors (GEF). The properties of two dominant-negative mutants within the catalytic domains of the ras-specific GEF, CDC25Mm, are described. In vitro, the mutant GEFW1056E and GEFT1184Eproteins are catalytically inactive, are able to efficiently displace wild-type GEF from p21ras, and strongly reduce affinity of the nucleotide-free ras·GEF complex for the incoming nucleotide, thus resulting in the formation of a stable ras·GEF binary complex. Consistent with their in vitro properties, the two mutant GEFs bring about a dramatic reduction in ras-dependent fos-luciferase activity in mouse fibroblasts. The stable ectopic expression of the GEFW1056Emutant in smooth muscle cells effectively reduced growth rate and DNA synthesis with no detectable morphological changes.
- [Show abstract] [Hide abstract] ABSTRACT: Interest in the production of L-(+)-lactic acid is presently growing in relation to its applications in the synthesis of biodegradable polymer materials. With the aim of obtaining efficient production and high productivity, we introduced the bovine L-lactate dehydrogenase gene (LDH) into a wild-type Kluyveromyces lactis yeast strain. The observed lactic acid production was not satisfactory due to the continued coproduction of ethanol. A further restructuring of the cellular metabolism was obtained by introducing the LDH gene into a K. lactis strain in which the unique pyruvate decarboxylase gene had been deleted. With this modified strain, in which lactic fermentation substituted completely for the pathway leading to the production of ethanol, we obtained concentrations, productivities, and yields of lactic acid as high as 109 g liter(-1), 0.91 g liter(-1) h(-1), and 1.19 mol per mole of glucose consumed, respectively. The organic acid was also produced at pH levels lower than those usual for bacterial processes.
- [Show abstract] [Hide abstract] ABSTRACT: Introduction of the Lactobacillus casei lactate dehydrogenase (LDH) gene into Saccharomyces cerevisiae under the control of the TPI1 promoter yielded high LDH levels in batch and chemostat cultures. LDH expression did not affect the dilution rate above which respiro-fermentative metabolism occurred (Dc) in aerobic, glucose-limited chemostats. Above Dc, the LDH-expressing strain produced both ethanol and lactate, but its overall fermentation rate was the same as in wild-type cultures. Exposure of respiring, LDH-expressing cultures to glucose excess triggered simultaneous ethanol and lactate production. However, the specific glucose consumption rate was not affected, indicating that NADH reoxidation does not control glycolytic flux under these conditions.
- [Show abstract] [Hide abstract] ABSTRACT: The role of two residues within the catalytic domain of CDC25Mm, a mouse ras-specific guanine nucleotide exchange factor (GEF), was investigated by site-directed mutagenesis. The function of the mutant proteins was tested in vivo in both a Saccharomyces cerevisiae cdc25 complementation assay and in a mammalian fos-luciferase assay, and in in vitro assays on human and yeast Ras proteins. Mutants CDC25Mm(E1048K) and CDC25Mm(S1122V) were shown to be (partly) inactive proteins, similar to their yeast homologs. Mutant CDC25Mm(S1122A) showed higher nucleotide exchange activity than the wild type protein on the basis of both in vitro and in vivo assays. Thus, alanine and valine substitutions at position 1122 within the GEF catalytic domain originate mutations with opposite biological properties, indicating an important role for position 1122 in GEF function.
- [Show abstract] [Hide abstract] ABSTRACT: The CDC25Mm gene codes for Ras-guanine nucleotide exchange factors. Four different full-length cDNA clones derived from the same gene and coding for proteins of different sizes that have in common the last 661 amino acids have been isolated from mouse brain. In order to investigate the expression of the products of this gene in different tissues we have prepared two polyclonal antibodies directed toward two different regions of the protein comprised in the last C-terminal 472 amino acids. While in most of the tested tissues we have been unable to definitely identify CDC25Mm products, in NIH3T3 fibroblasts we have found a poorly expressed 120-kDa protein. In the mouse brain we have identified two proteins of 140 and 58 kDa. While the former is expressed in the adult mouse, the latter is present in the embryo and persists for few days after birth. This finding suggests that differential expression of various forms of CDC25Mm may be involved in brain development.