Phosphorylation of the Spi-B transcription factor reduces its intrinsic stability

The Spi-B transcription factor is an Ets protein expressed in B lymphoid ce lls and closely related to the Spi-1/ PU.1 oncoprotein, By mutational analy sis, me showed that Spi-B is phosphorylated by casein kinase II in vitro on four serine residues. Mutation of these four serines to alanines prevented the phosphorylation of Spi-B in ave, increased the ability of Spi-B to tra nsactivate expression of a reporter gene and led to a decrease of Spi-B sta bility. We propose that the phosphorylation of Spi-B mag participate in the modulation of Spi-B functional activity by controlling its intracellular p rotein level. (C) 1999 Federation of European Biochemical Societies.