CHARACTERIZATION OF DIVERSE FUNCTIONAL ELEMENTS IN THE UPSTREAM SP1 DOMAIN OF THE RAT LUTEINIZING-HORMONE RECEPTOR GENE PROMOTER

Transcription of the luteinizing hormone receptor gene is dependent on Sp1-induced promoter activation from two Sp1 binding domains (Sp1(2) and Sp1(4)) within the 173-base pair promoter. Of the two Sp1 binding domains, the canonical GC box (GGGCGG) was determined by mutation to b e the binding element for only the Sp1(2) domain. The Sp1 binding elem ent within the Sp1(4) domain was identified by mutation and immunologi cal/competition studies as the 5'-GGG GTG GGG that conforms to a Zif-2 68 like three zinc finger binding domain, rather than the canonical 3' Sp1(4) GC box (GGGCGG). The guanines in the third trinucleotide (GGG GTG GGG) were not required for Sp1 binding, although they increased bi nding affinity, Non-Sp1 protein(s) bind the 3' Sp1(4), GC box, and by themselves exhibit transcriptional activity, Tissue specific differenc es were localized to this non-Sp1 binding domain, which functionally s ubstituted for the downstream activating M1 regulatory domain in non e xpressing but not in expressing cells, Mutations of both non-Sp1 and M 1 domains were required for inhibition of promoter activity in constru cts that retained the Sp1 binding elements in non expressing cells, in dicating that together these domains may play a role in regulation of luteinizing hormone receptor gene expression.