Multiple forms of tubulin in polytomella and chlamydomonas: evidence for a precursor of flagellar -tubulin

The quadriflagellate alga polytomella agilis contains several -tubulins with distinct isoelectric points (McKeithan, T.W., and J.L. Rosenbaum, 1981, J. Cell Biol., 91:352-360). While -3 is the major component in flagella, -1 predominates in cytoskeletal microtubules. For determination of whether the differences in - tubulins are due to distinct genes or to posttranslational modification of a common -tubulin precursor, poly A+ RNA was isolated from deflagellated and control (nonregenerating) cells and translated in vitro. Approximately twice as much -1 was synthesized using RNA from deflagellated as compared to control cells; however, there was no detectable synthesis in vitro of -3 in either. These results suggest that -3 tubulin is formed in vivo by posttranslational modification of a form co- migrating with, and possibly identical to, cytoskeletal -tubulin. In the related alga chlamydomonas reinhardii deflagellation greatly stimulates synthesis of tubulin and tubulin mRNA. As in polytomella, the principal -tubulin synthesized both in vivo and in vitro following deflagellation in chlamydomonas is more basic than the major -tubulin and appears to correspond to -1 tubulin in polytomella. The conversion of -1 to -3 receives additional support from in vivo labeling and pulse-chase experiments. In addition, in both polytomella and chlamydomonas some conversion of -1 to -3 appears to occur even when protein synthesis is inhibited.
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• Levilliers, N, Fleury, A, Hill, A. (1995). Monoclonal and polyclonal antibodies detect a new type of post-translational modification of axonemal tubulin. J. Cell Sci. 108: 3013-3028 [Abstract]  

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