General tubulin buffer (PEM). Contains 80 mM PIPES pH 6.9, 2 mM MgCl2 and 0.5 mM EGTA. Used as a tubulin working buffer in the form of G-PEM (i.e. PEM plus 1 mM GTP (Cat.# BST06)) or a tubulin polymerization buffer in the form of glycerol containing G-PEM (PEM plus 1 mM GTP (Cat. # BST06) and e.g. 5% glycerol (see Cat. # BST05)).