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

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