Normal yeast cells grow at 42°C. Five yeast haploid strains, with independent alleles of YFG1 having impaired cell growth at 42°C, were isolated and labeled as yfg1ts1 to yfg1ts5. A haploid (yfg1ts1) carrying a spontaneously generated mutation (sup1) at an independent locus was isolated, which can grow at 42°C. Using pairwise crossing, sup1 was introduced into strains carrying yfg1ts2 to yfg1ts5 alleles. All these haploids grew at 42°C.

Based on this data, the following statements were made to describe the Sup1-Yfg1 molecular/genetic interaction.

A. Sup1 codes for a protein which, when over-expressed, stabilized mutant yfg1ts proteins.
B. Sup1 codes for a protein that physically interacts with Yfg1 protein.
C. Sup1 protein upregulates an alternate pathway.
D. Sup1 is a nonsense suppressor that restores protein translation in cells carrying yfg1ts allele.

Which one of the following options represents the combination of all correct statements?

Correct option is C

EXPLANATION-

A. Sup1 codes for a protein which, when over-expressed, stabilizes mutant Yfg1ts proteins.
Possible mechanism of suppression. But not definitively supported by the data (no mention of protein stabilization or overexpression).
Uncertain — no direct evidence.

B. Sup1 codes for a protein that physically interacts with Yfg1 protein.
Also possible, but not proven by genetic suppression alone. Physical interaction is a strong claim and would need biochemical validation.
Speculative — no direct evidence.

C. Sup1 protein upregulates an alternate pathway.
Consistent with the idea of bypass suppression (a common mechanism of suppression). Plausible and commonly observed in suppressor genetics.
Likely correct.

D. Sup1 is a nonsense suppressor that restores protein translation in cells carrying yfg1ts allele.
Yfg1ts are temperature-sensitive missense mutations, not nonsense mutations. So a nonsense suppressor would not apply.
Incorrect.

Although A and B are speculative, if we go by the "most inclusive correct" answer based on what's plausible (not necessarily proven), option 3 is best supported from the given choices.

So, the correct option is (c) A, B and C only