Heterogeneous nuclear ribonucleoproteins (hnRNPs) are thought to be involved in pre-mRNA processing. However, its role in the regulation of gene expression is as yet poorly understood. Proteins of the heterogeneous nuclear ribonucleoparticles (hnRNP) family form a structurally diverse group of RNA binding proteins implicated in various functions. Recently, hnRNP proteins have been shown to hinder communication between factors bound to different splice sites. Conversely, several reports have described a positive role for some hnRNP proteins in pre-mRNA splicing. hnRNP-U, also termed scaffold attachment factor A (SAF-A), binds to pre-mRNA and nuclear matrix/scaffold attachment region DNA elements.