Question

4) Many mutant yeast strains have been isolated that are defective in cell cycle control. Two mutant strains affect the Gee and the Wee genes, but have different effects on the cell cycle. Gee have very short cell cycles and divide when they are much smaller than usual. Suggest what stages of the cell cycle may be affected by mutations in Gee or Wee and provide evidence for why that is the case Gee (5 pts) Wee (5 pts):

Answer 1

In the majority of yeast cells, the cell cycle is stringently controlled and is temperature sensitive i. e. cells will not undergo complete cell cycle in non-permissive temperatures. However, due to mutations control over cell cycle is not elicited. cdc and wee gene mutations are common among them.

Wee

Typically wee mutants are smaller than normal. One of the possible reason is wee proteins are involved in cell division prevention, i.e. wee proteins are checks to prevent cells from dividing when cells are too small.

Mutations in wee genes cause premature entry into cell division.

Wee mutations affect the loss of control over cell cycle prior to cell division. Thus affects G2 phase.

Mechanism of action: Wee genes are involved in temperature-dependent activation of mitosis promoting factor. Mutations in wee will activate MPF at any temperatures.

Gee

gee gene mutations lead to growth in cells but do not divide.

Gee gene mutations affect the late G2 phase and early M phase. Cells do not enter the mitotic phase.

Gee gene may be involved in G2 check point transients. Mutations, however, prevent from crossing checkpoint.