The egr-1 gene (also termed NGFI-A, zif/268 and Krox24) is predicted to encode a protein with three 'zinc finger' domains. Analogous DNA-binding motifs are present in several putative transcriptional regulatory proteins. The mRNA of egr-1 is rapidly and transiently induced by a variety of growth factors in diverse cell types. We have used a synthetic peptide corresponding to the C-terminus of the predicted egr-1 protein to generate mouse and rabbit polyclonal antibodies. These antibodies have been used to identify the egr-1 protein, designated p75egr-1, by immunoprecipitation, immunoblotting and immunocytochemical analyses. p75egr-1 is induced within 1-2 h of mitogenic stimulation and has a half-life of under 2 h. The protein is phosphorylated and has been localised to the nucleus by both immunocytochemical analysis and biochemical fractionation. The egr-1 protein is released from nuclei under isotonic or hypertonic salt conditions or by treatment with DNAase and binds double-stranded DNA in vitro. Consistent with the distribution described for the mRNA the egr-1 protein is abundantly expressed in normal rat brain.