Prometaphase

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In early prometaphase, the nuclear membrane has just degraded, allowing the microtubules to quickly interact with the kinetochores on the chromosomes, which have just condensed.

Microtubules invade the nuclear space.

In late prometaphase, most of the chromosomes have begun the events of metaphase while the rest should have at least have one kinetochore connected.

Prometaphase is the phase in between prophase and metaphase, in mitosis, in eukaryotic somatic cells. Microtubules which have radiated from the two centrosomes located at the opposite poles of the cells invading the nuclear space within it as the nuclear membrane dissolves, this process named open mitosis. This allows the double chromosomes within them to be distributed to the different locations of the cell by the microtubules without restriction. Some protists, such as algae, undergo a variation called closed mitosis where the microtubules are able to penetrate an intact nuclear envelope.

Following nuclear dissolution, kinetochores form at the centromeres of the chromosomes, with one for each chromatid. A kinetochore is a complex protein structure that is analogous to a ring for the microtubule hook; it is the point where microtubules attach themselves to the chromosome. Although the kinetochore is not fully understood, it is known that it contains a molecular motor. When a microtubule connects with the kinetochore, the motor activates, using energy from adenosine triphosphate to "crawl" up the tube toward the originating centrosome. The kinetochore provides the pulling force necessary to later separate the chromosome's two chromatids.

The microtubules are composed of two types, kinetochore microtubules and non-kinetochore microtubules. Kinetochore microtubules begin searching for kinetochores to attach to. A number of non-kinetochore microtubules find and interact with corresponding nonkinetochore microtubules from the opposite centrosome to form the mitotic spindle.

The role of prometaphase is completed when all of the kinetochore microtubules have attached to their kinetochores, upon which metaphase begins. An unattached kinetochore, and thus a non-aligned chromosome, even when most of the other chromosomes have lined up, will trigger the spindle checkpoint signal. This prevents premature progression into anaphase by inhibiting the anaphase-promoting complex until all kinetochores is attached and all the chromosomes aligned.

Early events of metaphase can coincide with the later events of prometaphase, as chromosomes with connected kinetochores will start the events of metaphase individually before other chromosomes with unconnected kinetochores that are still lingering in the events of prometaphase.