Cover photograph (Copyright © 2000, American Society for Microbiology. All rights reserved.): NXF proteins belong to a family of mRNA export factors having a conserved modular organization consisting of the following structural domains: a noncanonical RNP-type RNA-binding domain (yellow exons), four leucine-rich repeats (green exons), an NTF2-like domain that allows heterodimerization with a partner known as p15 (NXT) (red exons), and a ubiquitin-associated domain that mediates the interaction with nucleoporins (cyan exons). The background image shows the localization of human NXF3 fused to green fluorescence protein in transfected HeLa cells. The protein can be seen predominantly in the nucleoplasm. (See related article on page 8996.)