Yeast enzymes transcription factors

Another important requirement for the chosen bait protein is that it should not yield autoactivation of transcription factor activity. This may occur in the GAL4 and LexA systems if the bait actually is a transcription factor or if the bait mimics the transcription factor activity. Autoactivation is evident if the DNA-BD bait construct is cotransformed into competent yeast with an empty AD vector and the resultant transformants show reporter gene enzyme activities and growth on SD media. Obviously, this needs to be avoided because cDNA library screening with such a bait will result in the detection of many false positives. 

Fig. 1. Schematic overview of copper trafficking and homeostasis inside the yeast cell. The actions of Mad and Ace 1, copper-dependent metalloregulatory transcription factors, control the production of copper import [copper transporter (Ctr) and reductase (Fre)] and detoxification/sequestration [metallothionein (MT)] machineries, respectively. Three chaperone-mediated delivery pathways are shown. Atxl shuttles Cu(I) to the secretory pathway P-type ATPase Ccc2 (right). CCS delivers Cu(I) to the cytoplasmic enzyme copper-zinc superoxide dismutase (SOD) (left). Coxl7 shuttles Cu(I) to cytochrome c oxidase (CCO) in the mitochondria (bottom). Mitochondrial proteins Scol and Sco2 may also play a role in copper delivery to the CuA and CuB sites of CCO. Copper metabolism and iron metabolism are linked through the actions of Fet3, a copper-containing ferroxidase required to bring iron into the cell (lower right) (see text).

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