BRCA1/BARD1 ubiquitinate phosphorylated RNA polymerase II.
The breast- and ovarian-specific tumor suppressor BRCA1, when associated with BARD1, is an ubiquitin ligase. We have shown here that this heterodimer ubiquitinates a hyperphosphorylated form of Rpb1, the largest subunit of RNA polymerase II. Two major phosphorylation sites have been identified in the Rpb1 carboxyl terminal domain, serine 2 (Ser-2) or serine 5 (Ser-5) of the YSPTSPS heptapeptide repeat. Only the Ser-5 hyperphosphorylated form is ubiquitinated by BRCA1/BARD1. Overexpression of BRCA1 in cells stimulated the DNA damage-induced ubiquitination of Rpb1. Similar to the in vitro reaction, the stimulation of Rpb1 ubiquitination by BRCA1 in cells occurred only on those molecules hyperphosphorylated on Ser-5 of the heptapeptide repeat. In vitro, the carboxyl terminus of BRCA1 (amino acids 501-1863) was dispensable for the ubiquitination of hyperphosphorylated Rpb1. In cells, however, efficient Rpb1 ubiquitination required the carboxyl terminus of BRCA1, suggesting that interactions mediated by this region were essential in the complex milieu of the nucleus. These results link the BRCA1-dependent ubiquitination of the polymerase with DNA damage.
Starita
Lea M
LM
Program in Biology and Biomedical Sciences, Harvard Medical School, Boston, Massachusetts 02115, USA.
Horwitz
Andrew A
AA
Keogh
Michael-Christopher
MC
Ishioka
Chikashi
C
Parvin
Jeffrey D
JD
Chiba
Natsuko
N
D019313:BRCA1 Protein / Q000378:metabolism*; D002460:Cell Line; D004249:DNA Damage; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D010766:Phosphorylation; D010957:Plasmids / Q000378:metabolism; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D012319:RNA Polymerase II / Q000737:chemistry*; D012441:Saccharomyces cerevisiae / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D025521:Tumor Suppressor Proteins / Q000378:metabolism*; D025801:Ubiquitin / Q000737:chemistry / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
D019313:BRCA1 Protein; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin; D012694:Serine; C102449:BARD1 protein, human; D044767:Ubiquitin-Protein Ligases; D005982:Glutathione Transferase; D012319:RNA Polymerase II