Search

ABSTRACT The fission yeast PHO regulon genes pho1, pho84, and tgp1—encoding a cell surface-associated acid phosphatase (Pho1), a plasma membrane inorganic phosphate transporter (Pho84), and a plasma membrane glycerophosphocholine transporter (Tgp1)—are strongly upregulated in response to acute phosphate starvation, as are the SPBPB2B2.06c and SPAC1039.02 genes that encode putative 5'-nucleotidase paralogs of the binuclear metallophosphoesterase enzyme superfamily. Via proteomic analysis of the medium harvested from phosphate-replete and phosphate-starved fission yeast, we define a starvation secretome that includes SPBPB2B2.06c (renamed Efn1, for extracellular five-prime nucleotidase), SPAC1039.02 (henceforth Efn2), and Pho1 among the most abundant exported proteins elaborated by phosphate-starved cells. We demonstrate and characterize a 5'-nucleotidase activity secreted into the medium of phosphate-starved efn1+efn2+ cells, which is eliminated by simultaneous deletion of efn1 and efn2. By singly deleting efn1 and efn2, we find that Efn1 contributes the greater share of secreted 5'-nucleotidase activity. Efn1 and Efn2 catalyze the release of inorganic phosphate from all four standard ribonucleoside monophosphates, in order of preference: CMP > UMP > AMP > GMP. Whereas efn1+efn2+ cells can use extracellular CMP as a source of phosphate during phosphate starvation, efn1∆ efn2∆ cells cannot. The secretion of 5'-nucleotidase enzymes during phosphate limitation is a newly appreciated facet of fission yeast phosphate homeostasis.IMPORTANCESchizosaccharomyces pombe adapts to phosphate starvation by upregulating the expression of a cell surface acid phosphatase that mobilizes inorganic phosphate from the extracellular milieu, as well as transmembrane transporters that take up inorganic phosphate and glycerophosphocholine. This study identifies two paralogous extracellular 5'-nucleotidase enzymes, Efn1 and Efn2, encoded by genes that are highly transcriptionally induced during acute phosphate starvation, as major proteins secreted into the medium by phosphate-starved fission yeast cells. Secreted Efn1 and Efn2 catalyze the release of inorganic phosphate from all ribonucleoside monophosphates, with a preference for CMP. Secretion of Efn1 and Efn2 enables phosphate-starved fission yeast to thrive by using extracellular CMP as a source of inorganic phosphate. The starvation-induced production of extracellular 5'-nucleotidases adds a new layer of pro-adaptive function during phosphate limitation.

Between 1964 and 1985, a military dictatorship in Brazil combined an arsenal of political instruments—surveillance, violent repression, and propaganda, among others—to justify its illegal rule. How did the Brazilian military regime attempt to justify its claim to power for more than two decades? What discursive strategies did it use to win popular support, despite the violence it perpetrated? This paper investigates how discourse is used to legitimize power and create meaning in authoritarian regimes. Using ethnographic content analysis of archival materials, I pinpoint and analyze three key discursive frames employed in regime propaganda: "defenders of democracy," "Great Brazil" and "model citizenship." I argue that the Brazilian military regime used these frames to justify its authority, forge national values and social norms, and redefine the boundaries of the national community. These findings not only contribute to our understanding of authoritarian power that is wielded and legitimized through discourse, but also speak to the enduring consequences of authoritarianism in sociopolitical subjects. [ABSTRACT FROM AUTHOR]