Characterization of DNA binding properties of Yp20: an abundant nuclear protein isolated from Saccharomyces cerevisiae.

The aim of this study was to elucidate the function of Yp20 (yeast 20 kDa protein) which is an abundant basic DNA-binding protein copurified with yeast chromatin. The work presented here shows that Yp20 is a sequence specific DNA binding protein. DNA binding activity was extremely thermostable. The affinity of binding to TRP1 was higher than the affinity of binding to the B domain of ARS1. The dissociation half time of Yp20-DNA complexes was less than 1 min. Yp20 showed no homology to a similar abundant 21 kDa ARS binding factor II (ABFII), previously described. Competitive gel retardation assays revealed two different regions that were protected by Yp20. One was overlapping the ABF1 binding site on ARS1 and another protected region was found upstream to the translational start codon of the TRP1 gene. It thus appears that Yp20 may have a role in DNA replication and/or transcription.