Tubulohelical membrane arrays: novel association of helical structures with intracellular membranes.

A novel organelle-like membrane specialization has been found in an epithelial cell line. Characteristically, the helical membrane arrays (referred to hereafter as TUHMAs) are organized around tubular, proteinaceous electron-dense cores of 80 nm in diameter. Depending on the cell status, up to 8 of these cores provide the basis for an intermingled membrane scaffold of an overall length of 3-5 microm. TUHMAs exist as single organelles in transient association with the nucleus, the rough endoplasmic reticulum, patches of annulate lamellae, and the Golgi complex. While most of the constituents are still unknown, evidence for an involvement of nucleoporins in TUHMA organization is presented, as shown by fluorescence immunochemistry. This should make TUHMAs more easily accessible for future studies on their structure and function.