Is high mobility group protein 17 phosphorylated in vivo? re-examination of the HeLa cell cycle data

When in vivo [³²P] phosphate labeled HMG proteins from unsynchronized HeLa cells are separated by electrophoresis in acid-urea polyacrylamide gels, as opposed to separation in SDS-polyacrylamide, HMG 17 does not show any ³²P incorporation. Likewise, no ³²P radioactivity was found in HMG 17 protein isolated at different stages of the cell cycle from synchronized cells. By contrast, HMG 14 reveals a previously reported (Bhorjee, J.S. (1981) Proc. Natl. Acad. Sci. U.S.A. 78, 6944-6948) cell cycle stage-specific dependent phosphorylation with maximum ³²P radioactivity in the G₂ phase relative to G₁. Furthermore, HMG 14 is resolved into multiple electrophoretic forms as phosphoprotein in the acid-urea system. The results presented seriously question the data on the in vivo phosphorylation of HMG 17, and suggest that these be reevaluated.