title: Multiple forms of tubulin in Polytomella and Chlamydomonas: evidence for a precursor of flagellar alpha-tubulin.
abstract: The quadriflagellate alga polytomella agilis contains several alpha-tubulins with distinct isoelectric points (McKeithan, T.W., and J.L. Rosenbaum, 1981, J. Cell Biol., 91:352-360). While alpha-3 is the major component in flagella, alpha-1 predominates in cytoskeletal microtubules. For determination of whether the differences in alpha- tubulins are due to distinct genes or to posttranslational modification of a common alpha-tubulin precursor, poly A+ RNA was isolated from deflagellated and control (nonregenerating) cells and translated in vitro. Approximately twice as much alpha-1 was synthesized using RNA from deflagellated as compared to control cells; however, there was no detectable synthesis in vitro of alpha-3 in either. These results suggest that alpha -3 tubulin is formed in vivo by posttranslational modification of a form co- migrating with, and possibly identical to, cytoskeletal alpha-tubulin. In the related alga chlamydomonas reinhardii deflagellation greatly stimulates synthesis of tubulin and tubulin mRNA. As in polytomella, the principal alpha-tubulin synthesized both in vivo and in vitro following deflagellation in chlamydomonas is more basic than the major alpha-tubulin and appears to correspond to alpha-1 tubulin in polytomella. The conversion of alpha-1 to alpha-3 receives additional support from in vivo labeling and pulse-chase experiments. In addition, in both polytomella and chlamydomonas some conversion of alpha-1 to alpha-3 appears to occur even when protein synthesis is inhibited.
mesh_terms: D002696:Chlamydomonas / Q000378:metabolism*; D056890:Eukaryota / Q000378:metabolism*; D005407:Flagella / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D014404:Tubulin / Q000378:metabolism*
chemical_list: D011498:Protein Precursors; D014404:Tubulin