The yeast A kinases differentially regulate iron uptake and respiratory function - PubMed (original) (raw)

The yeast A kinases differentially regulate iron uptake and respiratory function

L S Robertson et al. Proc Natl Acad Sci U S A. 2000.

Abstract

Yeast has three A kinase catalytic subunits, which have greater than 75% identity and are encoded by the TPK genes (TPK1, TPK2, and TPK3) [Toda, T., Cameron, S., Sass, P., Zoller, M. & Wigler, M. (1987) Cell 50, 277-287]. Although they are redundant for viability, the three A kinases are not redundant for pseudohyphal growth [Robertson, L. S. & Fink, G. R. (1998) Proc. Natl. Acad. Sci. USA 95, 13783-13787; Pan, X. & Heitman, J. (1999) Mol. Cell. Biol. 19, 4874-4887]; Tpk2, but not Tpk1 or Tpk3, is required for pseudohyphal growth. Genome-wide transcriptional profiling has revealed unique signatures for each of the three A kinases leading to the identification of additional functional diversity among these proteins. Tpk2 negatively regulates genes involved in iron uptake and positively regulates genes involved in trehalose degradation and water homeostasis. Tpk1 is required for the derepression of branched chain amino acid biosynthesis genes that seem to have a second role in the maintenance of iron levels and DNA stability within mitochondria. The fact that TPK2 mutants grow better than wild types on nonfermentable carbon sources and on media deficient in iron supports the unique role of Tpk2 in respiratory growth and carbon source use.

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Figures

Figure 1

Figure 1

High-affinity iron uptake in yeast. Insoluble, extracellular Fe(III) is reduced to Fe(II) by the plasma membrane ferric reductases Fre1 and Fre2. Iron is then transported into the cell by a plasma membrane complex consisting of the multicopper oxidase Fet3 and the iron permease Ftr1. Ftr1 transports Fe(III), and Fet3 oxidizes Fe(II) to Fe(III) to allow transport by Ftr1. Fet3 requires copper for activity. The copper transporter Ccc2 is required for the copper-loading of Fet3 in the late Golgi.

Figure 2

Figure 2

Tpk2 negatively regulates genes involved in iron uptake. Total RNA was probed with FET3, FTR1, or SIT1 by Northern blotting. (Lane 1) 10560-2B (TPK). (Lane 2) LRY765 (tpk1). (Lane 3) LRY590 (tpk2). (Lane 4) LRY636 (tpk3).

Figure 3

Figure 3

Growth of TPK mutants on different media. Strains were grown on YPD (iron-rich, glucose medium), high-glucose/low-iron media (low iron), YPEG (ethanol glycerol medium), and YPEG containing the iron chelator ferrozine (+ferr). From the top, the strains are 10560-2B (wild type), LRY765 (tpk1), LRY590 (tpk2), and LRY636 (tpk3).

Figure 4

Figure 4

Model showing functional specificity of the three PKAs. See text for details.

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