​Two newly identified proteins, X and Y, are tested for sequence-specific DNA binding activity. The results of an electrophoretic mobility shift assay (EMSA) with a labeled DNA fragment and proteins X and Y in various combinations are shown below.​

​Poly dl:dC is a DNA duplex of polynosine and polycytosine. Which one of the following options represents the correct interpretation of the results obtained?​

Correct option is C

Stepwise Interpretation:

1. Lane 1 (DNA alone): Shows free DNA at the bottom, indicating no protein bound.

2. Lane 2 (DNA + X): Shift observed compared to free DNA — indicates X binds DNA.

3. Lane 3 (DNA + Y): Shift observed, but different from lane 2 — indicates Y binds DNA but differently from X.

4. Lane 4 (DNA + X + Y): Two distinct shifts are seen, representing X-DNA and Y-DNA complexes, suggesting both proteins bind DNA, but separately.

5. Lane 5 (DNA + Poly dI:dC): No shift, meaning Poly dI:dC alone doesn't bind DNA.

6. Lane 6 (DNA + X + Poly dI:dC): Shift reduced or lost compared to lane 2 — Poly dI:dC competes with DNA for X binding, indicating X is not sequence-specific (since Poly dI:dC is a nonspecific competitor).

7. Lane 7 (DNA + Y + Poly dI:dC): Shift still present despite competitor — indicating Y binds DNA in a sequence-specific manner, unaffected by nonspecific competitor.

Correct interpretation:

• X does not bind DNA in a sequence-specific manner (because Poly dI:dC competes and reduces binding).

• Y binds DNA in a sequence-specific manner (Poly dI:dC does not interfere).

Final answer:

Option 3: Both proteins bind to DNA but Y binds in a sequence-specific manner.