Fig. 1. Heterogeneous distribution of nuclear pores. (A1) Low-magnification image of asynchronous HeLa S3 nuclear surfaces stained for nuclear pores with anti-p62 antibody. Note that the nuclear pore distributions are surprisingly heterogeneous from nucleus to nucleus. Inset, visualization of single nuclear pores at high magnification. (A2) Nucleus with an almost uniform pore distribution. (A3) Nucleus with a large `island' that is devoid of nuclear pores. (B) Direct observation of nuclear pores and pore-free islands by scanning electron microscopy. A nuclear surface of freeze-fractured early G1 HeLaS3 cells (inset) and its enlarged image. Many nuclear pores are clearly visible. A large pore-free island is spread on the smooth inner nuclear envelope, demonstrating the integrity of the nuclear envelope.