The overall process of manufacturing a ribosome serves as a good example to describe Pamela Silver's research interests, because it encompasses many individual problems in the field of nuclear transport. This area of basic research has grown from a handful of investigators 17 years ago, when Silver entered it, to well over 100 labs worldwide by now. In the August 1 and the August 15 Genes and Development , the HMS professor of biological chemistry and molecular pharmacology and her colleagues report new findings about how the cell's nucleus exports material into the cytoplasm. In the past five years, researchers have recognized that transport of proteins and RNAs into and out of the nucleus is a wide-ranging process that underlies most of the cell's activities. For example, DNA replication requires the import of enzymes and the DNA-covering histone proteins.
Most protein translation occurs in the cytoplasm, requiring that RNAs be delivered there.
Yet scientists are only now beginning to realize that leaving the nucleus may be equally important, says Silver. But together, they ultimately help explain the making of a ribosome, one of the most labyrinthine nuclear transport tasks facing a cell. First, mRNA for these proteins is made in the nucleus, then exits to be translated into ribosomal proteins in the cytoplasm. These proteins re-enter the nucleus, where they are attached to rRNA molecules previously generated there. The resulting two ribosomal subunits then leave the nucleus again, to finally join into a whole ribosome out in the cytoplasm.