35 GAL11, GAL11P, and the Action of GAL4

Abstract

OVERVIEW
A transcriptional activator binds to DNA through a DNA-binding domain and activates transcription of a nearby gene through a separate activating region. According to the simplest version of this picture, both domains are located on a single polypeptide, but it is now clear that this is not always the case; we know of activators whose DNA-binding and activating regions, although working within the framework outlined above, are located on separate proteins which must both be present to activate transcription. Examples of activators with this and even more elaborate arrangements are discussed. In particular, we present a model for how the yeast activator GAL4 works in collaboration with GAL11 to produce a strong activator.

INTRODUCTION
GAL4 is an 881-amino-acid protein found in yeast that binds to specific DNA sequences and activates transcription of nearby genes. It contains a type of Zn-dependent DNA-binding domain at its amino-terminal end (Keegan et al. 1986; Johnston 1987; Pan and Coleman 1990) and two acidic activating regions (designated I and II in Fig. 1), either of which can activate transcription when fused to the DNA-binding domain (Ma and Ptashne 1987a). In yeast, the DNA-binding domain of GAL4 alone can bind to DNA but cannot activate transcription (Keegan et al. 1986; Ma and Ptashne 1987a; Sadowski et al. 1988; Gill et al. 1990), and a fusion protein bearing the activating regions of GAL4 attached to a heterologous DNA-binding domain, that of the bacterial repressor protein LexA, activates transcription when bound to Lex sites (Brent and Ptashne...