MacroH2A1.2 binds the nuclear protein Spop.

X-chromosome inactivation is a phenomenon by which one of the two X chromosomes in somatic cells of female mammals is inactivated for life. The inactivated X chromosomes are covered with Xist (X-inactive specific transcript) RNA, and also enriched with the histone H2A variant, macroH2A1.2. The N-terminal one-third of macroH2A1.2 is homologous to core histone H2A, but the function of the C-terminal two-thirds, which contains a basic, putative leucine zipper domain, remains unknown. In this study, we tried analyzing protein-protein interaction with a yeast two-hybrid system to interact with the nonhistone region of mouse macroH2A1.2. The results showed that macroH2A1.2 interacts with mouse nuclear speckled type protein Spop. The Spop protein has a unique composition: an N-terminal MATH, and a C-terminal BTB/POZ domain. Further binding domain mapping in a glutathione-S-transferase (GST) pull-down experiment revealed that macroH2A1.2 binds the MATH domain of Spop, which in turn binds to the putative leucine zipper domain of macroH2A1.2.