[Ultrastructure of the fungal nucleus. III. Genesis of the nucleus-associated organelle (NAO equals "KCE")].

The nucleus-associated organelle (NAO) is a structure, significant for division and motion of the fungal nucleus. In the basidiomycete Polystictus (equals Trametes) versicolor it is composed during somatic interphase of two globular entities (GE) and the connecting middle plate (MP). Its genesis is followed electron optically by analysing serial sections of preselected stages. Genesis is strictly determined by time and space. It starts with synthesis of the new MP a few minutes upon karyokinesis has been completed. Synthesis is localized in the area of contact between old GE and outer membrane of the nuclear envelope. After growing of the MP to its maximal size both new GE's develop from swellings at its ends. Old Ge's are dissolved during this developmental process. The period of genesis takes 30--40 min and fills one third of the cell cycle. A GE-field exhibits characteristic alterations throughout the formation of the NAO. It is composed of GE, periglobular zone, microtubules, and both caps of endoplasmic reticulum and multivesicular bodies.