Instability of the microtubules of the connecting cilia has been suggested as a cause or complicating factor in some cases of retinitis pigmentosa. These microtubules are highly acetylated on Lys40 of alpha-tubulin; the function of this acetylation is as yet unknown. We have described the case of an infertile male with a rod dominant retinal degeneration whose sperm flagella show severe morphological abnormalities and greatly reduced acetylation. Currently, the project is directed toward characterization of tubulin acetyltransferase (TAT) complex using bovine retina and brain as the source. Because of the restricted amount of this complex available and to the high level of N-terminal block ade of the polypeptides making up this complex, sequencing attempts have not yet been generally successful. However, recent availability of monoclonal antibodies to a variety of microtubule proteins has made possible identification of several components of the affinity- purified TAT complex by Western blot analysis. Of four micro tubule-binding proteins tested, tau protein was detected in both bovine brain and retina TAT complex as well as in the sperm flagella of the human subjects. MAP2 was found in the retinal complex and, in a truncated form, in the complex from Y-79 retinoblastoma cells. Kinesin, but not cytoplasmic dynein, was found in all TAT complexes tested, suggesting that kinesin may be involved in movement of the complex along he microtubule. TAT activity assays show that microtubule acetylation is reduced in the presence of agents such as taxol or nonhydrolyzable GTP analogs that stiffen microtubules, but endogenous acetylation of the complex, as seen in the acetylation of arresting in the retinal complex, is unaffected by these agents. Investigation of the role of kinesin on the transport and acetylation activity of the TAT complex are presently in progress. Identification of the acetyltransferase subunit is being approached by a blot overlay technique. Preliminary results suggest that sufficient activity remains after SDS-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting for detection.
