cdc25 and tyrosin-15

[jb0378]

I was given the following question:

The cdc25 gene of the fission yeast Saccharomyces pombe encodes a phosphatase which dephosphorylates the tyrosine 15 residue of the cyclin-dependent kinase (Cdk). Dephosphorylation of tyrosine-15 of Cdk activates its kinase activity.
You introduced a 2nd copy of the cdc25 gene under control of the Gal promoter. The Gal promoter is active when yeast cells are grown on media containing galactose and repressed in cells grown on media containing glucose. How will the presence of glucose or galactose affect the cell cycle progression in this strain of yeast?

I understand how cdc25 works to dephosphorylate tyrosine-15 which then causes MPF to be active. I understand how a gene would behave under the control of a Gal promoter. I don't understand what the introduction of a 2nd copy would cause. Can someone please explain this.

Thanks!

[kolean]

When there is no glucose in the media (-Glu) then the promoter will turn on and express your vector, which in this case is the cdc25. It will over produce this dephosphatase and the MPF will be active faster, which will push the cell cycle faster. It will push the cell into Mitosis faster than normal, causing the cell to not complete its acquistion of cellular materials and thus will not be of normal size when dividing. This produces the Wee phenotype in S. pombe.