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Given a context passage, generate a question from the passage such that its answer is shortest continous span from the passage.

Histone variant H2A.Z-containing nucleosomes exist at most eukaryotic promoters and play important roles in gene transcription and genome stability. The multisubunit nucleosome-remodeling enzyme complex SWR1, conserved from yeast to mammals, catalyzes the ATP-dependent replacement of histone H2A in canonical nucleosomes with H2A.Z. How SWR1 catalyzes the replacement reaction is largely unknown. Here, we determined the crystal structure of the N-terminal region (599-627) of the catalytic subunit Swr1, termed Swr1-Z domain, in complex with the H2A.Z-H2B dimer at 1.78 A resolution. The Swr1-Z domain forms a 310 helix and an irregular chain. A conserved LxxLF motif in the Swr1-Z 310 helix specifically recognizes the C helix of H2A.Z. Our results show that the Swr1-Z domain can deliver the H2A.Z-H2B dimer to the DNA-(H3-H4)2 tetrasome to form the nucleosome by a histone chaperone mechanism.
Output:

Show your work and conclude with the exact phrasing "Therefore, the final answer is [answer]." where [answer] is just the final number or expression that solves the problem.
user
Which protein mediates the replacement of H2A by H2A.Z in the yeast Saccharomyces cerevisiae?