The TATA-binding protein from Saccharomyces cerevisiae oligomerizes in solution at micromolar concentrations to form tetramers and octamers

Equilibrium analytical ultracentrifugation has been used to determine the s toichiometry and energetics of the self-assembly of the TATA-binding protei n of Saccharomyces cerevisiae at 30 degrees C, in buffers ranging in salt c oncentration from 60 mM KCl to 1 M KCl. The data are consistent with a sequ ential association model in which monomers are in equilibrium with tetramer s and octamers at protein concentrations above 2.6 mu M. Association is hig hly cooperative, with octamer formation favored by similar to 7 kcal/mol ov er tetramers. At high [KCl], the concentration of tetramers becomes negligi ble and the data are best described by a monomer-octamer reaction mechanism . The equilibrium association constants for both monomer <-> tetramer and t etramer <-> octamer reactions change with [KCl] in a biphasic manner, decre asing with increasing [KCl] from 60 mM to 300 mM, and increasing with incre asing [KCl] from 300 mM to 1 M. At low [KCl], similar to 3 mole equivalents of ions are released at each association step, while at high [KCl], simila r to 3 mole equivalents of ions are taken up at each association step. Thes e results suggest that there is a salt concentration-dependent change in th e assembly mechanism, and that the mechanistic switch takes place near 300 mM KCl. The possibility that this self-association reaction may play a role in the activity of the TATA-binding protein in vivo is discussed. (C) 1999 Academic Press.