 Fungi and some protists, such as algae or trichomonads, undergo a variation called "closed mitosis" where the spindle forms inside the nucleus, or the microtubules penetrate the intact nuclear envelope.In late prometaphase, "kinetochore microtubules" begin to search for and attach to chromosomal kinetochores.A "kinetochore" is a proteinaceous microtubule-binding structure that forms on the chromosomal centromere during late prophase.