Purification and characterization of the yeast rDNA binding protein REB1

In the yeast Saccharomyces cerevisiae, the ribosomal RNA genes are present in a single tandem array. A transcriptional enhancer element lies within the spacer region between each rRNA gene, 2.2 kilobases upstream from the transcription initiation site. We have identified previously two proteins, REB1 and REB2, that bind to specific sites within the enhancer (Morrow, B. E., Johnson, S. P., and Warner, J. R. (1989) J. Biol. Chem. 264, 9061-9068). REB1 binds also to a second, higher affinity site near the promoter, 210 base pairs upstream from the initiation site. This report describes the purification and further characterization of REB1. REB1 is a single polypeptide with an apparent molecular mass of 125,000 Da that binds to the sequence CCGGGTAA. It has been found to bind also within transcriptional control regions of several genes transcribed by RNA polymerase II, such as the UASG of the GAL1-GAL10 spacer. Immunoprecipitation analysis demonstrated that REB1 is phosphorylated.