Tyrosine phosphorylation of α tubulin in human T lymphocytes

N-terminal sequencing of the 55- and 50-kDa polypeptides affinity purified on a phosphotyrosine monoclonal antibody column from activated Jurkat T cells identified α and β tubulin. Two-dimensional gel analysis indicated that α tubulin was directly phosphorylated on tyrosine. β Tubulin was not detectably tyrosine phosphorylated but was precipitated by anti-phosphotyrosine (PTyr) antibody by virtue of its association with the α subunit as a heterodimer. Phosphotyrosyl α tubulin was not incorporated into intact microtubules and was all in the unpolymerized soluble fraction. These results suggest that tyrosine phosphorylation of α tubulin may inhibit the ability of this subunit to polymerize into microtubules. Stimulation of Jurkat T cells via T cell receptor increased the amount of tubulin precipitated by the anti-PTyr antibody. These data raise the possibility that the polymerization of tubulin heterodimers may be regulated by phosphorylation on tyrosine during T cell activation.