The association of heterotrimeric GTP-Binding protein (Go) with microtubules

The heterotrimeric GTP-binding regulatory proteins (G proteins) play an important role in the regulation of membrane signal transduction. Recently, we identified the association of Go protein with mitotic spindles. Here we have investigated the relationship between Go protein and microtubules. We used temperature-dependent reversible assembly and taxol methods to purify microtubules from bovine brains. Go alpha, and G beta proteins were identified in the microtubular fraction by both methods. The Go alpha subunit in the microtubular fraction could be ADP ribosylated by pertussis toxin. Co-immunoprecipitation data also revealed that Go protein can interact with microtubules. Exogenous Go protein could be incorporated into the assembled microtubular fraction, and 5 mug/ml (60 nM) of Go protein inhibited 40% of microtubule assembly. Western blot analysis of Go alpha -1 and Go alpha -2 in microtubular fractions showed that only Go alpha -1 is associated with microtubules. We conclude that the Go alpha -1 beta gamma proteins are associated with microtubules and may play some role in regulating the assembly and disassembly of microtubules. Copyright (C) 2001 National Science Council, ROC and S. Karger AG, Basel.