Question

You engineer yeast cells that express the M cyclin during S phase by replacing the promoter sequence of the M cyclin gene with that of S cyclin. Keeping in mind that yeast cells have one common Cdk that binds to all cyclins, which of the following outcomes is least likely during this experiment? (a) There will be both M cyclin-Cdk and S cyclin-Cdk complexes in the cell during S phase.(b) Some substrates that are normally phosphorylated in M phase will now be phosphorylated in S phase.(c) G1 cyclins will be expressed during S phase.(d) S-Cdk targets will be phosphorylated during S phase.

Answer 1

The least likely outcome of engineering yeast cells to express M cyclin during S phase is G1 cyclins being expressed during S phase, as this procedure does not affect G1 cyclin expression.

Step-by-step explanation:

In an experiment where yeast cells are engineered to express M cyclin during S phase by replacing the M cyclin gene promoter with that of S cyclin, the least likely outcome would be (c) G1 cyclins being expressed during S phase. Changing the promoter of M cyclin to that of S cyclin does not affect G1 cyclin expression. Therefore, only the expression pattern of M cyclin would change, leading to the presence of both M cyclin-Cdk and S cyclin-Cdk complexes during the S phase, resulting in some substrates normally phosphorylated in M phase being phosphorylated in S phase instead. Importantly, S-Cdk targets would surely be phosphorylated during S phase, as this is a normal occurrence.

Answer 2

(c) G1 cyclins will be expressed during the S phase

Step-by-step explanation:

In those cases in which G cyclins are constitutively expressed, the G1 phase will be shortened