A widespread transposable element masks expression of a yeast copper transport gene.

Abstract

The trace element copper (Cu) is essential for cell growth. In this report we describe the identification of a new component of the high-affinity Cu transport machinery in yeast, encoded by the CTR3 gene. Ctr3p is a small intraceUular cysteine-rich integral membrane protein that restores high-affinity Cu uptake, Cu, Zn superoxide dismutase activity, ferrous iron transport, and respiratory proficiency to strains lacking the CTR1 (Cu transporter 1) gene. In most commonly used Saccharomyces cerevisiae laboratory strains, expression of CTR3 is abolished by a Ty2 transposon insertion that separates the CTR3 promoter from the transcriptional start sites by 6 kb. In strains that do not possess a Ty2 transposon at the CTR3 locus, expression of CTR3 is repressed by copper and activated by copper starvation. In such strains inactivation of both CTRI and CTR3 is required to generate lethal copper-deficient phenotypes. Although Ctrlp and Ctr3p can function independently in copper transport, the expression of both proteins provides maximal copper uptake and growth rate under copper-limiting conditions. These results underscore the importance of mobile DNA elements in the alteration of gene function and phenotypic variation.

h CTR1 : A human gene for copper uptake identified by complementation in yeast

“…The CCC2 protein is both functionally and structurally similar to the gene products defective in Menkes syndrome and Wilson disease described above. Although no mammalian copper uptake gene has been isolated, in yeast three copper uptake genes, CTR1, CTR2, and CTR3, have been identified (18)(19)(20). CTR1 and CTR3 are high-affinity copper transport proteins, and mutations in both CTR1 and CTR3 are required to eliminate high-affinity copper uptake in yeast.…”

“…CTR1 and CTR3 are high-affinity copper transport proteins, and mutations in both CTR1 and CTR3 are required to eliminate high-affinity copper uptake in yeast. In many laboratory strains, CTR3 function is interrupted by a Ty2 transposable element, and thus CTR1 alone becomes indispensable for high-affinity copper uptake for these laboratory strains (20). CTR2, whose sequence is similar to CTR1, appears to be a low-affinity copper uptake protein (19).…”

Dynamic Regulation of Copper Uptake and Detoxification Genes in Saccharomyces cerevisiae

“…Elegant genetic screens have identified genes that are responsible for Cu uptake under nutritional conditions when essential levels of Cu ions are present in the cell (10,25), distribution to appropriate subcellular compartments (8,15,31,49), and detoxification under toxic conditions when Cu ions are present in excess (7,40,41,45). At the nutritional level, Cu uptake into yeast cells is mediated by two membrane-associated high-affinity Cu(I) transporters, encoded by CTR1 and CTR3 (10,25), and a cell surface Cu(II)/Fe(III) reductase, encoded by the FRE1 gene, which reduces Cu(II) to Cu(I) prior to uptake (14,21). In the presence of excess Cu ions, when expression of the high-affinity Cu(I) transporters is abolished, Cu ion uptake can proceed through a putative low-affinity Cu ion uptake system.…”

Copper supplementation increases yeast life span under conditions requiring respiratory metabolism

“…The promoter of the gene for the high affinity copper transporter, Ctr3, has been shown to contain an insertion of the transposon Ty2 in many laboratory strains, including S288c and BY4742, a derivative of S288c (Knight et al, 1996). This insertion separates the promoter and start point of transcription from the CTR3 gene by 6 kb.…”