DNA ELEMENTS REGULATING ALPHA-1-TUBULIN GENE INDUCTION DURING REGENERATION OF EUKARYOTIC FLAGELLA

Eukaryotic flagella are complex organelles composed of more than 200 p olypeptides. Little is known about the regulatory mechanisms governing synthesis of the flagellar protein subunits and their assembly into t his complex organelle. The unicellular green alga Chlamydomonas reinha rdtii is the premier experimental model system for studying such cellu lar processes, When acid shocked, C. reinhardtii excises its flagella, rapidly and coordinately activates transcription of a set of flagella r genes, and ultimately regenerates a new flagellar pair, To define fu nctionally the regulatory sequences that govern induction of the set o f genes after acid shock, we analyzed the alpha 1-tubulin gene promote r. To simplify transcriptional analysis in vivo, we inserted the selec table marker gene, ARG7 on the satire plasmid with a tagged alpha 1-tu bulin gene and stably introduced it into C. reinhardtii cells. By dele tion of various sequences, two promoter regions (-176 to -122 and -85 to -16) were identified as important for induction of the tagged alpha 1-tubulin gene, Deleting the region between -176 and -122 from the tr anscription start site resulted in an induction level which was only 4 5 to 70% of that of the resident gene, Deleting the region upstream of -56 resulted in a complete lass of inducibility without affecting bas al expression, The alpha 1-tubulin promoter region from -85 to -16 con ferred partial acid shock inducibility to an arylsulfatase (ARS) repor ter gene, These results show that induction of the alpha 1-tubulin gen e after acid shock is a complex response that requires diverse sequenc e elements.