Endogenous galactoside-binding lectins (galectins) have been implicated in cell adhesion, growth, differentiation, neoplastic transformation, and metastasis. Galectin-1 (gal-1), one member of this family, has been best characterized. We isolated a DNA clone containing the gal-1 gene from mouse genomic libraries, and the sequence of the 5' upstream region up to -2430 bp was determined. Our previous study showed that sodium butyrate (butyrate) induced expression of gal-1 at both mRNA and protein levels in the murine embryonal carcinoma (EC) cell line PCC4.aza1R and the induction of gal-1 by butyrate in PCC4.aza1R cells is at least partially regulated at transcriptional level. To locate the region which is responsible for the induction of gal-1 by butyrate, transient transfection of PCC4.aza1R cells with a series of gal-1 promoter/CAT chimeric gene, which have different deletions of the 5' region of the gal-1 promoter, showed that this 2430 bp sequence is a butyrate-inducible promoter, and butyrate-inducible ability remained when only a 62 bp sequence ahead of the transcription site (+1) existed. The sequence from -62 to -41 which contains an Sp1 site at -57 was important for the induction of gal-1 expression by butyrate. Gel shift assay indicated that transcription factor SP1 actually bound to that Sp1 site. The changes of two nucleotides within that Sp1 site, from GG to TT, abolished the nuclear proteins binding to that Sp1 site as well as the response to butyrate. These results suggest that the 5' proximal Sp1 site at -57 is crucial for the butyrate-induced expression of the gal-1, and the direct binding of SP1 to this Sp1 site may be involved in this induction.