CLONING AND CHARACTERIZATION OF THE ACTIN-ENCODING GENE OF CHLAMYDOMONAS-REINHARDTII

The genomic and complementary DNA sequences were determined for the un ique actin-encoding gene in Chlamydomonas reinhardtii (Cr). The deduce d amino acid (aa) sequence of this actin was similar to most known act in sequences, with the highest identity (98.1%) being with that of Vol vox carteri actin. The Cr actin-encoding gene has one intron in the 5' -untranslated region and eight introns in the coding region. The latte r eight introns occur at the same positions as those in the V. casteri actin-encoding gene. The 5'-upstream region contains four short stret ches of sequence similar to the so-called 'tub box', a characteristic sequence proposed to be responsible for the regulation of synthesis of various axonemal proteins upon deflagellation and during the cell cyc le, Southern blot analysis indicated that the Cr genome has only a sin gle actin-encoding gene. An antibody specific for the 11-aa peptide co rresponding to the N-terminal sequence of this actin was found to reac t with a 43-kDa protein associated with flagellar inner-arm dynein. Th ese findings indicate that a single actin functions in both the cytopl asm and flagella of this organism.