Drosophila melanogaster contains a set of polypeptides capable of polymerizing into intermediate-like filaments.

A partial purification scheme applied to the Triton X-100 insoluble pellet of adult flies homogenates yielded a fraction which upon polymerization reproducibly produces filaments which in the electron microscope have all the typical properties of intermediate filaments. This is the first report of the presence of protein components with such properties in Drosophila. Thus, it is highly possible that insects and arthropodes, like other lower invertebrates, may contain the third extremely insoluble element of the cellular cytoskeleton.