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The constitutively active form of human Rac1 protein contains a glutamine to leucine substitution at residue 61. The common name for this mutant is Rac1(Q61L) or L61Rac1. The leucine substitution prevents endogenous and GAP-stimulated GTPase activity of Rac1, hence the protein is always in the active, GTP-bound, state. A similar mutation in Ras (Ras(Q61L)) behaves as an oncogenic mutation.
Rac1(Q61L) has been expressed in a bacterial system. The protein is supplied as a lyophilized powder. When it is reconstituted in distilled water to 1 mg/ml, the protein is in the following buffer: 2 mM Tris pH 7.6, 0.5 mM MgCl2, 0.5% sucrose and 0.1% dextran. Protein concentration is determined by the Precision Red Advanced Protein Assay Reagent (Cat. # ADV02).
The recombinant protein is 25 kDa, consisting of the 22 kDa Rac1 constitutively active protein plus a histidine tag in the amino-terminus.
For other forms of Rac1 as well as many other purified small G-proteins, see our main small G-protein product page.
Protein purity is determined by scanning densitometry of Coomassie Blue stained protein on a 12% polyacrylamide gel. His-Rac1(Q61L) protein was determined to be 90% pure.
Figure 1: His-Rac1(Q61L) protein purity determination. A 10 µg sample of R6101 (His-Rac1(Q61L) molecular weight approx. 25 kDa) was separated by electrophoresis in a 12% SDS-PAGE system, and stained with Coomassie Blue.
His-Rac1(Q61L) mutant protein binds GTP but its intrinsic GTPase activity has been eliminated, resulting in a constitutively active protein. The biological assay for His-Rac1(Q61L) activity consists of a pulldown assay using PAK-PBD beads (Cat. # PAK02). The PAK protein is an effector of Rac1 and will specifically bind to active GTP-Rac1. Stringent quality control ensures that > 80% of His-Rac1(Q61L) protein can be pulled down using this method.
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Storey, N. M., O'Bryan, J. P. and Armstrong, D. L. (2002). Rac and Rho mediate opposing hormonal regulation of the ether-a-go-go-related potassium channel. Curr. Biol. 12, 27-33.