MOLECULAR-CLONING OF LSIRF, A LYMPHOID-SPECIFIC MEMBER OF THE INTERFERON REGULATORY FACTOR FAMILY THAT BINDS THE INTERFERON-STIMULATED RESPONSE ELEMENT (ISRE)

Interferon regulatory factor (IRF) genes encode a family of DNA-bindin g proteins that are involved in the transcriptional regulation of type -I interferon and/or interferon-inducible genes. We report here the ch aracterization of LSIRF, a new member of the IRF gene family cloned fr om mouse spleen by the polymerase chain reaction using degenerate prim ers. LSIRF was found to encode a 51 kDa protein that shares a high deg ree of amino acid sequence homology in the DNA-binding domain with oth er IRF family members. LSIRF expression was detectable only in lymphoi d cells. In contrast to other IRF genes, LSIRF expression was not indu ced by interferons, but rather by antigen-receptor mediated stimuli su ch as plant lectins, CD3 or IgM crosslinking. In in vitro DNA binding studies, LSIRF was able to bind to the interferon-stimulated response element (ISRE) of the MHC class I promoter. The expression pattern and DNA binding activities suggest that LSIRF plays a role in ISRE-target ed signal transduction mechanisms specific to lymphoid cells.