Nucleopore. Within the nuclear membrane of the cell there are small holes, or pores, that allow the very selective transport of nucleic acids and proteins into and out of the cell nucleus. The material found in the cell nucleus is distinct from the material found in the cytoplasm. And these nucleopores, which are of regulated size, allow for the very selective transport of nucleic acids and proteins into and out of the cell nucleus. We used to think that it was a regulated process of how nucleic acids such as mRNAs moved out of the cell nucleus, and recently we've become more aware that there also is a regulated process by which cells transport proteins and nucleic acids into the nucleus, so this is a dynamic process.Julie A. Segre, Ph.D.