Phosphatase activity of PP2A in studies involving a second known binding partner of tAg, the JCV agnoprotein [40]. We were surprised to identify two LxCxE motifs that had been overlooked in the unique region of the JCV tAg; one of these sites is also found in BKV but neither site resides in the corresponding SV40, WUV, KIV or MCV polyomavirus proteins. As predicted, JCV tAg binds members of the re