Several M-CAT elements are present in the chicken nicotinic acetylcholine receptor γ-subunit promoter and required for the totipotency of this gene.To understand the binding properties of M-CAT element,the interaction of M-CAT motif,at the position -67/-61 relative to the initiation site of γ-promoter with nuclear proteins,were analyzed.Mutageneses and binding experiments demonstrated that the M-CAT core motif bound nuclear protein (s) from tested chicken tissues to generate a high-mobility complex;while the flanking sequence bound different factors to generate lower-mobility complexes with the exception of liver.Southwestern blotting showed that only a 30 kD protein was expressed in tested tissues of chicken embryo at day 13.These results suggest that a 30 kD factor can directly bind to M-CAT element in the manner of monomer,even homodimer and is ubiquitously expressed in tissues,while the binding of the factor(s) to flanking sequence should probably rely on the presence of a 30 kD ubiquitous factor.