Correct option is B
Explanation -
Statement A: Activity of maturation promoting factor (MPF) rises and falls in synchrony with the concentration of cyclin B.
True
MPF is a complex of Cyclin B and Cdk1 (Cyclin-dependent kinase 1). Cyclin B accumulates during G2 phase and is degraded during anaphase. MPF activity directly depends on Cyclin B levels.
So, as Cyclin B levels rise and fall, MPF activity also rises and falls accordingly.
Statement B: Cdc25 phosphatase mediates removal of phosphate from the inhibitory tyrosine residue (Y15) to yield highly active MPF.
True
Cdk1 is kept inactive by phosphorylation at Tyr15 and Thr14. Cdc25 is a phosphatase that removes the inhibitory phosphates, particularly from Tyr15, activating Cdk1. Once Cdk1 is dephosphorylated and bound to Cyclin B, it becomes highly active MPF.
Statement C: MPF specifically phosphorylates and depolymerizes lamin A and C, but not lamin B.
False / Misleading
During mitosis, MPF phosphorylates all three lamins: A, B, and C, leading to nuclear envelope disassembly. The statement incorrectly says that MPF does not phosphorylate lamin B, which is not true. Lamin B may behave differently (e.g., remains associated with nuclear membranes), but it is phosphorylated.
Statement D: MPF phosphorylates H1 histone.
True
Histone H1 is involved in higher-order chromatin structure. MPF phosphorylates H1 during mitosis, which contributes to chromatin condensation. While not a major MPF target compared to nuclear lamins or microtubule-associated proteins, this is a documented function.
Statement E: In Schizosaccharomyces pombe, overproduction of Wee1 protein decreases the length of G₂ phase and extends the period of M phase by functioning as a mediator of MPF activity.
False
Wee1 is a kinase that inhibits MPF activity by phosphorylating Cdk1 on Tyr15. Overexpression of Wee1 leads to G2 arrest or lengthening of G2, not shortening it.
This statement is opposite to reality — Wee1 delays entry into mitosis rather than promoting it.
So, the correct option is b - (A, B, and D)
