To study the chromatin remodeling complex SWR1, a researcher has prepared arrays of nucleosomes on long DNA strands that have been immobilized on magnetic beads. These nucleosomes are then incubated with an excess of the H2AZ-H2B dimer (which contains the histone variant H2AZ) in the presence or absence of SWR1 with or without ATP. She then separates the bead-bound nucleosomes (bound fraction) from the rest of the mix (unbound fraction) using a magnet, elutes the bound fraction from the beads, and performs SDS-PAGE on the samples. This is followed by a Western blot using an antibody specific to the H2AZ protein used in this experiment. The results are shown below, with the presence (+) or absence (-) of ATP, SWR1, or the H2AZ-H2B dimer in each incubation reaction indicated at the top of the corresponding lane.
Which of the following statements is confirmed by the Western blot shown?

Question

To study the chromatin remodeling complex SWR1, a researcher has prepared arrays of nucleosomes on long DNA strands that have been immobilized on magnetic beads. These nucleosomes are then incubated with an excess of the H2AZ-H2B dimer (which contains the histone variant H2AZ) in the presence or absence of SWR1 with or without ATP. She then separates the bead-bound nucleosomes (bound fraction) from the rest of the mix (unbound fraction) using a magnet, elutes the bound fraction from the beads, and performs SDS-PAGE on the samples. This is followed by a Western blot using an antibody specific to the H2AZ protein used in this experiment. The results are shown below, with the presence (+) or absence (-) of ATP, SWR1, or the H2AZ-H2B dimer in each incubation reaction indicated at the top of the corresponding lane. 
Which of the following statements is confirmed by the Western blot shown?

Quizplus · Accepted Answer

Remodeling complexes can catalyze the exchange of histone subunits (including the histone variants) in nucleosomes with the help of histone chaperones. In this experiment, addition of the SWR1 complex and ATP in the presence of excess H2AZ-H2B dimers results in the appearance of H2AZ-containing nucleosomes in the arrays, i.e. a band appears for the bound fraction. This indicates that the SWR1 complex transfers the H2AZ histones to the immobilized nucleosomes. There is no reason to believe that the antibody binds to the SWR1 complex.

To Study the Chromatin Remodeling Complex SWR1, a Researcher Has