Nucleopores of the giant amoeba, Pelomyxa carolinensis.

Abstract

As shown in tangential sections of Pelomyxa carolinensis nuclei, there are many pores, each with a surrounding annulus. Each annulus is composed of 8 subannuli or satellites, plus one to three central granules. Each satellite is an electron opaque mass (of much smaller opaque particulates) about 25 nm in diameter. The outer diameter of each annulus is about 115 nm while the inner, or pore diameter, is about 65 nm. The pores occur at distances averaging 185 nm from center to center. Frequently, delicate filaments connect adjacent satellites, and the central granule with the satellites. As seen in cross sections of the nucleus, nucleopores are formed by the fusion of the inner and outer nuclear envelope membranes. The pore appears as a gap, spanned by a delicate diaphragm anchored to the nuclear envelope where its two membranes are fused. Possible functions of the pore-annulus complexes are discussed.