Control of induction of tubulin synthesis in Chlamydomonas reinhardi

REMOVAL of the flagella from the biflagellate alga Chlamydomonas reinhardi results in the rapid production of new flagella 1–3 . Flagellar regeneration is 80–85% complete within 60 min (Fig. 1). Indirect evidence obtained from in vitro translation of polyribosomes and mRNA from deflagellated gametes 1 has indicated that flagellar regeneration is accompanied by a strong but transient induction of tubulin synthesis. Kinetic analysis showed that tubulin mRNA could be detected in polyribosomes in as little as 15 min after deflagellation. Since the cytoplasm contains a reserve of tubulin of sufficient size to supply at least one-third to one-half of the tubulin subunits required for flagellar reassembly 1,3 , the rapid initiation of tubulin synthesis following deflagellation suggested the existence of a highly sensitive system for detecting and responding to the cell's anticipated need for additional tubulin. As an approach to seeking such a mechanism, we have carried out studies to determine if the depletion of tubulin reserves during flagellar outgrowth might provide the signal for the induction of tubulin synthesis. We present here two types of experimental evidence which clearly demonstrate that the induction of tubulin synthesis is independent of the utilisation of tubulin reserves during flagellar regeneration.