Pericentriolar material (PCM, sometimes also called pericentriolar matrix) is an amorphous mass of protein which makes up the part of the animal centrosome that surrounds the two centrioles. The PCM contains proteins responsible for microtubule nucleation and anchoring including ?-tubulin, pericentrin and ninein.
Although the PCM appears amorphous by electron microscopy, Super-resolution microscopy finds that it is organized. The PCM have 9 fold symmetry that mimics the symmetry of the centriole. Some PCM Proteins are organized such that one end of the protein is found near the centriole and the other end is farther away from the centriole. The PCM size is dynamic during the cell cycle. After the cell division the PCM size is reduced in a process named Centrosome Reduction. During the G2 phase of the cell cycle the PCM size grow in a process named centrosome maturation.