Repressible Phosphatase Research Articles

Rpl12p affects the transcription of the PHO pathway high‐affinity inorganic phosphate transporters and repressible phosphatases

The ribosomal protein Rpl12p of Saccharomyces cerevisiae is encoded by duplicated genes, RPL12A and RPL12B. The gene products possess an identical amino acid sequence. Yeast strain 6EA1, which lacks both genes, is viable but exhibits a very slow-growth phenotype. In this study, 6EA1 cells were transformed with plasmids carrying either RPL12A or RPL12B, and the transcriptional profiles of wild-type W303, 6EA1 and the transformed cells grown in synthetic complete medium were examined by microarray analysis. Transcription of PHO84, a gene encoding a high-affinity phosphate transporter, was drastically suppressed in 6EA1. PHO84 expression is induced under phosphate-limiting conditions. Therefore, cells were grown in low-phosphate medium and transcripts encoding the PHO pathway proteins were quantified by qRT-PCR. The high-affinity phosphate transporters and repressible phosphatases were suppressed, while PHO4, a PHO pathway transcription activator, was upregulated in 6EA1. Accordingly, phosphate transport and acidic phosphatase activities were significantly decreased in 6EA1. Addition of RPL12A or RPL12B to 6EA1 largely lessens these effects. We postulate that RPL12 has an extra-ribosomal function in modulating the transcription of genes that need Pho4p activation.

Hydrolysis of RNA monomers by extracts of Aspergillus niger NRRL3.

Extracts of Aspergillus niger NRRL3 catalyzed dephosphorylation of AMP, GMP, CMP and UMP over a wide range of pH values from pH 1.5 to pH 10. They also catalyzed hydrolytic deamination of only cytidine out of the tested ribonucleotides, ribonucleosides and bases. Neither cleavage of the N-glycosidic linkages of these nucleotides nor those of the corresponding nucleosides could be effected by the extracts. Phosphate liberation from the four RNA monomers seemed to be effected by two phosphate-non repressible phosphatases, acid and alkaline. Optimum activity of the acid phosphatase with all the substrates was at pH2 and 40 degrees C while that of the alkaline phosphatase was at pH8 and 40 degrees-70 degrees C. Affinities of both phosphatases for the different ribonucleotides were in the order of magnitude AMP, CMP and phph > GMP > UMP. Freezing and thawing of the extracts had no effect either on the activities of two phosphatases or on that of the aminohydrolase. However, heating the extracts at 55 degrees for 25 min, in absence of the substrate, inactivated the phosphatases and had no effect on the deaminase. No evidence for the involvement of specific nucleotidases in ribonucleotides dephosphorylation was recorded.

Control and localization of the phosphatases in conidia of Neurospora crassa

Repressible acid, repressible alkaline, and constitutive alkaline phosphatases were studied with respect to their control and localization in conidia of Neurospora crassa. In contrast to constitutive alkaline phosphatase, the production and secretion of repressible phosphatases is regulated by phosphate level and pH of the culture medium. Phosphatase activity increased with conidial germination and was detectable partially in the growth medium after 5 h incubation. These enzymes were found to be located in different cell compartments. Part of the whole cell enzyme activity involved a soluble exoconidial fraction, and another part, a cell-bound enzyme that remained after successive washes. The cell-bound enzyme was sensitive to treatment with dilute acid and was thought to be located in the mural space. A third part of the enzyme activity was judged to be intracellular, as shown by treatments with surface-active agents and heat, which disrupted the conidia or destroyed the conidial permeability barriers. On the basis of these criteria, the constitutive alkaline phosphatase was considered to be more cryptic than the repressible phosphatases. The alkaline phosphatases were also active during heat treatment, suggesting they may be involved in the mechanism of secretion.Key words: Neurospora crassa, repressible acid phosphatase, repressible alkaline phosphatase, constitutive alkaline phosphatase, conidia.

Phosphatase activity in Eutrophic Tokyo Bay

Alkaline phosphatase activity in seawater samples taken from Tokyo Bay was measured by both spectrophotometric and fluorometric methods. A stratified distribution pattern of the enzyme was observed in August, a vertically mixed pattern in December. The distribution of phosphatase activity in the eutrophic seawater was paralleled by variations in other parameters, such as viable counts of bacteria, chlorophyll a content, inorganic and total phosphorus concentrations, amounts of seston, particulate deoxyribonucleic acids (DNA) and protein. A significant correlation between phosphatase activity and these measurements indicated that the enzyme was a good indicator of the degree of eutrophication. The positive relationship between phosphatase and inorganic phosphorus indicates that enzyme activity was not inhibited at inorganic phosphorus levels present in the bay and that production of phosphatase by microorganisms inhabiting the bay was not repressed at the inorganic phosphorus levels in the bay. Culture experiments revealed that the formation of repressible phosphatase by bacteria isolated from the bay was not affected by the inorganic phosphorus levels in the bay.

Synchronous Cultures of Chlamydomonas reinhardti: Properties and Regulation of Repressible Phosphatases

Abstract De novo synthesis of phosphatase (derepression) in orthophosphate deprived synchronously growing Chlamydomonas reinhardti has been demonstrated by using a double labelling isotope technique coupled with cellulose acetate electrophoresis. Repressed and derepressed phosphatase exhibited different enzymatic properties as pH optimum, electrophoretic pattern, Km and Ki values. Especially the acid phosphatase was located near the cell surface.Inorganic, cold TCA‐extractable 32P, decreased during the first 1–2 h after phosphate deprivation when there was little or no net synthesis of phosphatase.Results of experiments with additions of orthophosphate and cycloheximide to derepressed cells, indicated that the derepressible enzyme was relatively unstable, while its m‐RNA was relatively stable.

Genetic control of the synthesis of repressible phosphatases in Neurospora crassa.

Genetic control of the synthesis of repressible phosphatases in Neurospora crassa.