Precursors of the nerve growth factor γ subunit and renin bind to microtubules

Abstract

Translation products of a reticulocyte lysate reaction, programmed with poly(A)-rich RNA from the male mouse submaxillary gland, were subjected to affinity chromatography on a tubulin-Sepharose column. Analysis of the bound proteins in sodium dodecylsulfate/polyacrylamide gels revealed 2 polypeptides of MW 27,000 and 45,000, that were shown to bind to tubulin in a specific manner. These polypeptides were absent from the translation products coded by poly(A)-rich RNA from the female mouse. They were eluted from the tubulin-Sepharose resin under conditions similar to those employed for the dissociation of immune complexes. The MW-27,000 and MW-45,000 proteins were identified by immunoprecipitation with specific antisera as the precursors of the .gamma. subunit of the nerve growth factor (NGF) and renin, respectively. These 2 precursors as well as a 3rd, unidentified polypeptide of MW 38,000, probably unrelated to the .beta. subunit of NGF, bound also to microtubules. The mature from of renin, purified from the submaximillary gland, also displayed an affinity for the microtubules. In contrast, the mature form of the .gamma. subunit of NGF did not bind to the microtubules. The possible involvement of the microtubules (tubulin) in the biosynthesis of these 2 secretory proteins is discussed.