PHOSPHORYLATION OF NUCLEAR AND FLAGELLAR BASAL APPARATUS PROTEINS DURING FLAGELLAR REGENERATION IN CHLAMYDOMONAS-REINHARDTII

The antiphosphoprotein monoclonal antibody MPM-2 was used to investiga te protein phosphorylation during flagellar regeneration in Chlamydomo nas reinhardtii. MPM-2 recognizes a phosphorylated epitope and detects several Chlamydomonas proteins by Western immunoblot analysis. Two MP M-2 reactive proteins (34 and 90 kD) increase in Western immunoblot in tensity after flagellar excision and decrease in intensity during flag ellar regeneration. Immunofluorescence and immunogold labeling reveale d MPM-2 staining within the nucleus, especially towards the nuclear pe riphery, the flagellar basal apparatus, and the nucleus-basal body con nector after flagellar excision. Comparison of MPM-2 reactivity in wil d-type cells and in the mutant bald-2, which lacks functional basal bo dies, demonstrates that the 34-kD protein is localized in the nucleus and the 90-kD protein is localized in the flagellar basal region. MPM- 2 reactivity is observed in cells competent for flagellar regeneration . However, when cells were treated with the kinase inhibitor, staurosp orine, MPM-2 reactivity did not increase after flagellar excision and flagellar regeneration was impaired. These observations suggest that p hosphorylation of the 34- and 90-kD proteins may be important for flag ellar regrowth. Possible roles for phosphorylation in flagellar regene ration include transcriptional activation and transport of flagellar p recursors to the base of the growing flagella.