The nucleus is not the only place where genetic instructions are pieced together. Messenger RNA, or mRNA, which conveys DNA instructions to the rest of the cell, is made of genetic sequences that, when spliced together properly, code for proteins. The many ways in which mRNA sequences can be woven back together help to create the body's vast diversity of proteins. Scientists thought that splicing took place only in the nucleus. Now, using fluorescent tags on splicing proteins in rat studies, molecular neurobiologist Jim Eberwine of the University of Pennsylvania and his colleagues have found that the process also occurs outside the nucleus—in particular, in dendrites, which are branches off neurons that help the cells receive electrical messages. Eberwine speculates that dendrites save mRNA in an unspliced form to ensure that the proteins they encode are not manufactured until needed. The findings appear in the November 15, 2005, Proceedings of the National Academy of Sciences USA.
This article was originally published with the title "Protein by the Splice" in Scientific American 294, 1, 32 (January 2006)