evidence that recombinant Pak0 could phosphorylate Cortactin at S000. As there are no available phospho S000 antibodies, the authors might instead IP Cortactin from p00-/- MEFs and blot with p-Ser antibodies or, better, ID sites by mass spec. I know this sort of experiments isn\'t fun or easy, but the use of phospho-mimics alone is not adequate to support their conclusions.