A SEQUENCE-SPECIFIC SINGLE-STRAND DNA-BINDING PROTEIN THAT CONTACTS REPRESSOR SEQUENCES IN THE HUMAN GM-CSF PROMOTER

NF-GMb is a nuclear factor that binds to the proximal promoter of the human granulocyte-macrophage colony stimulating factor (GM-CSF) gene. NF-GMb has a subunit molecular weight of 22 kDa, is constitutively exp ressed in embryonic fibroblasts and binds to sequences within the adja cent CK-1 and CK-2 elements (CK-1/CK-2 region), located at approximate ly -100 in the GM-CSF gene promoter. These elements are conserved in h aemopoietic growth factor (HGF) genes. NF-GMb binding requires the pre sence of repeated 5'CAGG3' sequences that overlap the binding sites fo r positive activators. Surprisingly, NF-GMb was found to bind solely t o single-strand DNA, namely the noncoding strand of the GM-CSF CK-1/CK -2 region. NF-GMb may belong to a family of single-strand DNA binding (ssdb) proteins that have 5'CAGG3' sequences within their binding site s. Functional analysis of the proximal GM-CSF promoter revealed that s equences in the -114 to -79 region of the promoter containing the NF-G Mb binding sites had no intrinsic activity in fibroblasts but could, h owever, repress tumour necrosis factor-alpha (TNF-alpha) inducible exp ression directed by downstream promoter sequences (-65 to -31). Subseq uent mutation analysis showed that sequences involved in repression co rrelated with those required for NF-GMb binding.