MEC-12, an alpha-tubulin required for touch sensitivity in C-elegans

mec-12 is one of a dozen genes required for touch receptor neuron function in Caenorhabditis elegans, Some mec-12 mutants (mechanosensory-defective) l ack the large-diameter microtubules that are characteristic of these neuron s (15 protofilaments, as opposed to 11). Mutants of mec-7, a beta-tubulin e ncoding gene, have a similar phenotype, We have identified the nature of me c-12 by germline transformation rescue and characterization of a point muta tion. Sequence analysis of the mec-12 encoded product (MEC-12) indicates th at it corresponds to a novel C.elegans alpha-tubulin, MEC-12 is the only id entified C. elegans alpha-tubulin that contains a lysine at position 40, a known site of post-translational acetylation. Some mec-12 mutations elimina te microtubule acetylation as assayed immunocytochemically; phenotypic resc ue using a MEC-12 variant lacking the lysine-40 showed that acetylation is not required for MEC-12 activity. Although functionally needed only in the touch neurons, mec-12 is expressed in several other neuron types. These res ults support the notion that tubulin isotype diversity contributes to the f ormation of distinct classes of microtubules; 15-protofilament microtubule assembly requires MEC-12 alpha-tubulin and MEC-7 beta-tubulin, which are bo th highly expressed in the touch receptor neurons. MEC-12 is the first repo rted alpha-tubulin isotype that appears to be required in a single class of neuronal microtubules.