Figure 3.

Sumoylation of Nab contributes to SUMO recruitment to chromatin and modulates Krox20 transcriptional activity. (A) Levels of small ubiquitin-like modifier 1 (SUMO1) associated with the Id4 promoter were determined by chromatin immunoprecipitation experiments in P19 cells transfected with Flag-tagged wild-type Nab or the KR2 mutant or not transfected (−). Levels of SUMO were determined on cells growing normally (white bars) or subjected to serum stimulation (black bars). Fold increase in SUMO levels were normalized to the value determined in non-transfected untreated cells. Flag levels were also determined as a control (grey bars) and fold increase was normalized to the value of Nab-transfected cells. (B) A lacZ reporter construct responsive to Krox20 was tested in P19 cells cotransfected with the indicated expression constructs. Relative units of β-galactosidase (β-gal) were normalized to the value of cells cotransfected with Krox20 alone (100%). Values are means of three independent experiments±s.d.