Interphase cells of the centric diatom, Thalassiosira fluviatilis, lack detyrosinated, nontyrosinatable and acetylated tubulin.

Within eukaryotic cells tubulin generally exists in protein families composed of closely related isoforms generated either by differential gene transcription or by posttranscriptional and posttranslational mechanisms. In this study, immunological approaches were used to examine the contribution of posttranslational modifications to tubulin heterogeneity in a centric diatom, Thalassiosira fluviatilis, and to show the spatial distribution of microtubules in these cells during their interphase. After blotting to nitrocellulose, tubulin in cell-free homogenates of T. fluviatilis was recognized by several general tubulin antibodies including one to the tyrosinated isoform, but not by antibodies to detyrosinated, nontyrosinatable nor acetylated tubulins. Immunofluorescent staining of methanol-fixed cells revealed a net-like reticulum of microtubules originating at or near the cell nucleus. For all antibodies, except one (TU-01), results obtained by immunofluorescent experiments corrobated the analysis of blotted tubulins. Furthermore, microtubules exhibited differential staining patterns corresponding to the intensity of antibody reactivity on blots. Antibody to detyrosinated tubulin, as well as TU-01, yielded a spotty pattern of fluorescence on chloroplasts. Microtubules in T. fluviatilis support normal cell function in the absence of detectable amounts of three common posttranslationally modified tubulins, perhaps due to the rigid silica frustule which maintains shape and to the absence of flagella in interphase cells.