Practice question

Histone octamer contains flexible unstructured N-terminal tails and protruding C-termini extending beyond DNA gyres. These lysine, arginine and serine rich segments undergo extensive covalent post-translational modifications including acetylation, methylation, phosphorylation, ubiquitination and sumoylation catalyzed by writer enzymes and erased by erasers. Modifications alter electrostatic charge and create binding sites for effector proteins containing bromodomains, chromodomains and PHD fingers, forming combinatorial histone code that governs accessibility, transcription activation, repression, replication timing and DNA repair without altering fundamental histone DNA wrapping structure.