During prophase, which is the first stage of mitosis, the chromosomes condense and become thousands of times more compact than they were during interphase. Each duplicated chromosome consists of two identical sister chromatids joined at a point called the centromere, and these structures now appear as X-shaped bodies when viewed under a microscope. The condensed sister chromatids are then held together at the centromere, which is a DNA sequence to which proteins bind to form the kinetochore, the site of eventual attachment of the spindle microtubules. Several DNA binding proteins catalyze the condensation process, including cohesin and condensin. Cohesin forms rings that hold the sister chromatids together, whereas condensin forms rings that coil the chromosomes into highly compact forms. The mitotic spindle also begins to develop during prophase. As the cells two centrosomes move toward opposite poles, microtubules gradually assemble between them, forming the network that will later pull the duplicated chromosomes apart. When prophase is complete, the cell enters prometaphase, the second stage of mitosis.