Ki-67/MKI67 is an antigen which is expressed during G1, S, G2, and M phases of the cell cycle (mitotically active cells), but not during G0 phase (resting cells). It is a large protein with expected molecular weight of about 395 kDa, and it has a very complex localization pattern within the nucleus, one which changes during cell cycle progression. During interphase, Ki-67 antigen can be exclusively detected in the nucleus, whereas in mitotic phase, most of Ki67 pool gets relocated to the chromosomal surface.
