INTERPHASE CELLS OF THE CENTRIC DIATOM, THALASSIOSIRA-FLUVIATILIS, LACK DETYROSINATED, NONTYROSINATABLE AND ACETYLATED TUBULIN

Within eukaryotic cells tubulin generally exists in protein families c omposed of closely related isoforms generated either by differential g ene transcription or by posttranscriptional and posttranslational mech anisms. In this study, immunological approaches were used to examine t he contribution of posttranslational modifications to tubulin heteroge neity in a centric diatom, Thalassiosira fluviatilis, and to show the spatial distribution of microtubules in these cells during their inter phase. After blotting to nitrocellulose, tubulin in cell-free homogena tes of T. fluviatilis was recognized by several general tubulin antibo dies including one to the tyrosinated isoform, but not by antibodies t o detyrosinated, nontyrosinatable nor acetylated tubulins. Immunofluor escent staining of methanol-fixed cells revealed a net-like reticulum of microtubules originating at or near the cell nucleus. For all antib odies, except one (TU-01), results obtained by immunofluorescent exper iments corrobated the analysis of blotted tubulins. Furthermore, micro tubules exhibited differential staining patterns corresponding to the intensity of antibody reactivity on blots. Antibody to detyrosinated t ubulin, as well as TU-01, yielded a spotty pattern of fluorescence on chloroplasts. Microtubules in T. fluviatilis support normal cell funct ion in the absence of detectable amounts of three common posttranslati onally modified tubulins, perhaps due to the rigid silica frustule whi ch maintains shape and to the absence of flagella in interphase cells.