One of several features acquired by chromatin of the inactive X chromosome (Xi) 
is enrichment for the core histone H2A variant macroH2A within a distinct 
nuclear structure referred to as a macrochromatin body (MCB). In addition to 
localizing to the MCB, macroH2A accumulates at a perinuclear structure centered 
at the centrosome. To better understand the association of macroH2A1 with the 
centrosome and the formation of an MCB, we investigated the distribution of 
macroH2A1 throughout the somatic cell cycle. Unlike Xi-specific RNA, which 
associates with the Xi throughout interphase, the appearance of an MCB is 
predominantly a feature of S phase. Although the MCB dissipates during late S 
phase and G2 before reforming in late G1, macroH2A1 remains associated during 
mitosis with specific regions of the Xi, including at the X inactivation center. 
This association yields a distinct macroH2A banding pattern that overlaps with 
the site of histone H3 lysine-4 methylation centered at the DXZ4 locus in Xq24. 
The centrosomal pool of macroH2A1 accumulates in the presence of an inhibitor of 
the 20S proteasome. Therefore, targeting of macroH2A1 to the centrosome is 
likely part of a degradation pathway, a mechanism common to a variety of other 
chromatin proteins.