We previously detected Roc-Cullin interactions in vivo by immunoprecipitating Flag-tagged Roc1a, Roc1b, and Roc2 proteins from transgenic embryo extracts and identifying interacting proteins by mass spectrometry [25]. For these experiments, each Roc protein was expressed using the ubiquitous Roc1a promoter [24]. The data indicated that Roc1a bound Cul1-4 and that Roc2 bound Cul5, but could not eli