CHARACTERIZATION OF HMBP-2, A DNA-BINDING PROTEIN THAT BINDS TO HIV-1LTR WHEN ONLY ONE OF THE 3 SP1 SITES IS METHYLATED

HIV-1 methylation binding protein-1 (HMBP-1) (formerly called HMBP) is a protein found in human cell nuclei that binds with enhanced affinit y to a fragment of the HIV-1 long terminal repeat sequence (LTR) conta ining three Sp1 sites when all three sites are methylated. HMBP-2 is a nother protein present in the nuclei of human T helper lymphocytes and HeLa cells that binds to the HIV-1 LTR. HMBP-2 binds preferentially t o the same region of the HIV-1 LTR as does HMBP-1, but HMBP-2 binds be st when only one of the three Sp1 sites is methylated. HMBP-2 can be s eparated from HMBP-1 chromatographically, and dimethyl sulfate (DMS) m ethylation interference analysis indicates that their binding sites ar e not identical. HMBP-2 represents a novel protein factor capable of b inding to a partially methylated region of the HIV-1 LTR.