Coordinate regulation of the four tubulin genes of Chlamydomonas reinhardi

Abstract

During cell division and during the induction of tubulin synthesis that accompanies flagellar regeneration in Chlamydomonas reinhardi, four tubulin mRNAs of discrete molecular sizes are produced. During induction two beta tubulin mRNAs (2.47 kb and 2.34 kb) and two alpha tubulin mRNAs (2.26 kb and 2.13 kb) are synthesized in high abundance and in a closely coordinated fashion. Combined data from restriction enzyme mapping (i.e., Southern analysis) of genomic DNA and of Charon 30 recombinant clones bearing inserts of Chlamydomonas tubulin genes provide direct evidence for four distinct tubulin genes in this organism. Dot-blot analysis of the level of hybridization of a 32p nick-translated beta tubulin cDNA to genomic DNA from gametic cells and to a clone containing the beta 1 tubulin gene indicate that each beta 1 tubulin gene is present in one copy per cell. Additional hybridization experiments employing fragments of cDNA clones which selectively anneal to either the 3' or 5' portions of the two alpha tubulin genes or to one or both of the two beta tubulin genes suggest that each tubulin gene is actively transcribed to give rise to one of the four tubulin mRNAs. These observations further suggest that at most four basic types of tubulin subunits are produced by Chlamydomonas and that the heterogeneity of tubulin subunits reported to exist in the flagellar axoneme must arise as a result of post-translational modification.