The nucleolar transcription factor mUBF is phosphorylated by casein kinase II in the C-terminal hyperacidic tail which is essential for transactivation.
UBF is a DNA binding protein which interacts with both the promoter and the enhancer of various vertebrate ribosomal RNA genes and functions as a transcription initiation factor for RNA polymerase I (pol I). We have purified murine UBF to apparent molecular homogeneity and demonstrate that its transactivating potential, but not its DNA binding activity, is modulated in response to cell growth. In vivo labelling experiments demonstrate that UBF is a phosphoprotein and that the phosphorylation state is different in growing and quiescent cells. We show that UBF is phosphorylated in vitro by a cellular protein kinase which by several criteria closely resembles casein kinase II (CKII). A major modification involves serine phosphoesterifications in the carboxy terminal hyperacidic tail of UBF. Deletions of this C-terminal domain severely decreases the UBF directed activation of transcription. The data suggest that phosphorylation of UBF by CKII may play an important role in growth dependent control of rRNA synthesis.
Voit
R
R
Institute of Cell and Tumor Biology, German Cancer Research Center, Heidelberg.
Schnapp
A
A
Kuhn
A
A
Rosenbauer
H
H
Hirschmann
P
P
Stunnenberg
H G
HG
Grummt
I
I
D000595:Amino Acid Sequence; D000818:Animals; D047390:Casein Kinase II; D002460:Cell Line; D002466:Cell Nucleolus / Q000378:metabolism; D002872:Chromosome Deletion; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D035463:Pol1 Transcription Initiation Complex Proteins; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012318:RNA Polymerase I / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D015183:Restriction Mapping; D013379:Substrate Specificity; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation
D004268:DNA-Binding Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; C063844:transcription factor UBF; D004247:DNA; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D012318:RNA Polymerase I