Transcriptional repressor which binds to the consensus sequence 5'-GGTGTG-3'. May play a role in the cell cycle regulation (By similarity). Plays a role in the regulation of the circadian clock; binds to the GC box sequence in the promoter of the core clock component ARTNL/BMAL1 and represses its transcriptional activity. Regulates the circadian expression of genes involved in lipogenesis, gluconeogenesis, and glycolysis in the liver. Represses the expression of PCK2, a rate-limiting step enzyme of gluconeogenesis. By TGF-beta and GDNF. Expressed in a circadian manner in the liver with a high at ZT14-18 and a low at ZT2 (at protein level). Expressed in a circadian manner in the bone, kidney and skeletal muscle. Up-regulated in response to glucose. Ubiquitinated; mediated by SIAH1 and leading to its subsequent proteasomal degradation. Male mice display postprandial and fasting hyperglycemia while female mice are normoglycemic but display higher plasma triglycerides. Belongs to the Sp1 C2H2-type zinc-finger protein family.