Figure 1. Thermal regulation of gene expression by the H2A.Z protein.

a, At lower temperatures, an H2A.Z-containing nucleosome is appropriately positioned just downstream of the transcriptional start site (TSS) of many genes. The average occupancy of this nucleosomal protein on a given gene reflects the balance between its deposition by the SWR1 chromatin-remodelling complex and its eviction driven by the RNA polymerase II (Pol II) enzyme or the action of chromatin-remodelling enzymes [sentence OK?]. The presence of H2A.Z-containing nucleosomes might help to maintain gene expression at a level appropriate to lower ambient temperature. b, As temperatures rise, the thermal instability of H2A.Z pushes the equilibrium towards its loss; nucleosomes containing only the H2A histone protein, however, remain unaffected. Depletion or modification of H2A.Z-carrying nucleosomes with rising temperature might allow gene-specific regulatory mechanisms to increase or decrease the expression of specific gene as needed to adapt the plant to the higher temperatures. Thus, through its unique thermal instability, H2A.Z might act as a gatekeeper of the temperature response.