A NOVEL NUCLEAR-PROTEIN BINDS CENTROMERIC ALPHA-SATELLITE DNA

We have previously reported the identification of a naturally occurrin g junction between alpha satellite and satellite III DNA on human chro mosomes 13, 14 and 21 (1). Direct sequence analysis has shown that the 9 bp alphoid-derived direct repeat sequence (GTGAAAAA-G) present at t he junction is fully conserved on these chromosomes. A novel protein, pJ alpha, present in HeLa nuclear extracts, binds to the conserved jun ction sequence. Mutation analysis of the binding site suggests that pJ alpha can recognize one of the two 9 bp repeats and provides some ins ight into nucleotides that are important for binding. Competition stud ies support the possibility that this protein binds a significant port ion of genomic alpha satellite DNA. Preliminary protein purification e xperiments have shown that pJ alpha has a molecular weight of 10 - 15 kDa.