Practice question

Structural analysis shows octamer built from central tetramer plus peripheral dimers. H2A and H2B heterodimerize via histone fold domains creating handshake arrangement stabilized by antiparallel helices and hydrophobic core. Two such dimers flank tetramer symmetrically contacting outer DNA superhelical turns near entry exit. This dimeric form exchanges dynamically during transcription, removed by remodeling complexes and chaperones NAP1, FACT enabling polymerase passage. H3-H4 interaction forms tetramer, cross combinations like H2B-H3 or H1-H2A incompatible due to sequence specificity, confirming H2A-H2B as physiological dimer.