The biological functions of DNA and RNA are dependent upon highly specific and complex interactions with proteins. Elucidation of the mechanisms by which proteins recognize and manipulate nucleic acids in such fundamental processes as transcription, translation, replication, and recombination remains an area of intense research activity in structural biology. Despite recent progress, the enormous diversity of protein-nucleic acid interactions means that many questions of fundamental importance remain to be answered. Multi-dimensional NMR methods will be used to investigate the mechanisms by which certain key eukaryotic regulatory proteins containing zinc finger motifs, which are the predominant mediators of protein. Nucleic acid interactions in eukaryotes, can recognize diverse RNA targets and regulate gene expression at the post-transcriptional level. The Wilms tumor suppressor protein (WT 1) is essential for normal mammalian urogenital development and plays a critical role in sex determination. It regulates gene expression through interactions with both DNA and RNA, mediated by its four zinc fingers. The solution structure of the complex formed between the -KTS splice variant of WT1 and an RNA aptamer will be determined to obtain fundamental insights into the mechanism by which the zinc finger motif is able to recognize both RNA and DNA. A novel family of double stranded RNA-binding zinc finger proteins mediates the p53 tumor suppressor response, induces apoptosis, and inhibits tumor cell growth. The structure of a domain of the human p53-induced protein wig-1 will be determined, both free and bound to dsRNA, to obtain insights into the mechanism by which these zinc fingers bind preferentially to the A-form helix. A number of single-stranded RNA binding proteins that mediate gene expression at the post-transcriptional level contain CCCH zinc fingers. These proteins function in cellular differentiation and in regulation of tumor necrosis factor-alpha by destabilization of its mRNA. The structure of the human TIS 11 d CCCH domain bound to an AU-rich single stranded RNA recognition element will be determined to obtain insights into the mechanism by which it recognizes specific mRNA regulatory sites and regulates gene expression at the post-transcriptional level. This research will provide novel insights into the mechanisms by which the ubiquitous zinc finger motifs interact with and recognize diverse RNA targets, and will form the foundations for a structure-based description of the role of zinc finger proteins in post-transcriptional regulation of gene expression.