Question

16. You have cloned a centromere from yeast. You have also identified three genes, X, Y and Z that code for proteins that are a subset of the kinetochore proteins that are bound to the centromere. None of your three genes is essential but each does contribute to the overall efficiency of chromosomal segregation. You raise antibodies to each of your three proteins. You also contstruct four strains, a wild-type strain, a strain in which gene X is deleted (XD), a strain in which gene Y is deleted (YD), and a strain in which gene X is deleted (XD). You perform a series of ChIP experiments in each of your four strains. You obtain the data shown in the figure below.

In each strain, you perform a ChIP experiment using the antibody to protein X (AbX, lane 1), or the antibody to protein Y (AbY, lane 2) or the antibody to protein Z (AbZ, lane3). Which of the following diagrams best represents the arrangement of your proteins at the centromere? The line in these diagrams represents the centromeric DNA.

AbX Aby Abz AbX Aby AbZ Wild-type AbX Aby AbZ YA AbX Aby AbZ ZA XA

Answer 1

Ans: Chromatin immunoprecipitation (ChIP) is a technique that determines whether a protein of interest interacts with a specific DNA sequence.

Now as given in the question that in X(D) the X gene is deleted and we do not get any bands in all the respective lands and this represents that X protein is directly bound with the protein and because of its absence no other protein is detected in ChIP. In second strain the gene Y is deleted and we do not get any band in 2nd and 3rd lane and in the third strain the gene Z is deleted and we do not get any band in 3rd lane. So from second and third ChIP we can conclude that Y is after the X gene and Z is after the Y gene as in the second strain after deletion of Y gene we do not get any band in both AbY and AbZ column which means that deletion of Y will affect the binding of Z to the X protein.

So the arrangement of proteins at centromere is as follows:

X protein is directly bound to the centrosome, Y protein is bound to the X protein and Z proteim is bound to the Y protein.

Hence option F is correct.