Proof of de novo synthesis of the qa enzymes of Neurospora crassa during induction
AUTOR(ES)
Reinert, William R.
RESUMO
In Neurospora crassa three inducible enzymes are necessary to catabolize quinic acid to protocatechuic acid. The three genes encoding these enzymes are tightly linked on chromosome VII near methionine-7 (me-7). This qa cluster includes a fourth gene, qa-1, which encodes a regulatory protein apparently exerting positive control over transcription of the other three qa genes. However, an alternative hypothesis is that the qa-1 protein simply activates preformed polypeptides derived from the three structural genes. The use of density labeling with D2O demonstrated conclusively that the qa enzymes are synthesized de novo only during induction on quinic acid. Native catabolic dehydroquinase (5-dehydroquinate dehydratase; 5-dehydroquinate hydro-lyase, EC 4.2.1.10) (a homopolymer of ca 22 identical subunits) has a density of 1.2790 g/cm3 as determined by centrifugation in a modified cesium chloride density gradient. Growth in H2O followed by induction in 95% D2O shifts the density of the enzyme to 1.3130 g/cm3, indicating de novo synthesis during induction. In the reciprocal experiment, i.e., growth in 80% D2O followed by induction in either 95% D2O or H2O, the densities of catabolic dehydroquinase were 1.3135 and 1.2800 g/cm3, respectively. Because growth on D2O does not affect the density of the H2O-induced enzyme, there can be no significant synthesis of catabolic dehydroquinase prior to induction. Similar results were obtained for a second qa enzyme, quinate dehydrogenase (quinate:NAD+ oxidoreductase, EC 1.1.1.24). Thus, induction of two qa enzymes involves de novo protein synthesis, not enzyme activation or assembly.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=431918Documentos Relacionados
- Induction and de novo synthesis of uricase, a nitrogen-regulated enzyme in Neurospora crassa.
- Genetic regulation of the qa gene cluster of Neurospora crassa: induction of qa messenger ribonucleic acid and dependency on qa-1 function.
- Genetic evidence on the organization and action of the qa-1 gene product: a protein regulating the induction of three enzymes in quinate catabolism in Neurospora crassa.
- Synthesis of Signals for De Novo DNA Methylation in Neurospora crassa
- Induction of Neurospora crassa Laccase with Protein Synthesis Inhibitors