Prometaphse
Prometaphse is a phase of mitosis following prophase and preceeding metaphse in which the nuclear envelope breaks down and chromosomes first attatch to spindle fibers.
Prometaphase starts abruptly with the breakdown of the nuclear evelope freeing sister chromatids, this is necessary for the separation of genetic material into two new cells later on in mitosis.The chromosomes now attatch to spindle microtubules via their kinetochores and can now undergo active movement.
References : Alberts et al (2008) The molecular biology of the cell, 5th edition, Garland science, New York