Kinase activities in the non-histone chromosomal proteins of resting and proliferating BHK21 C13 cells.

The in vitro polymerization of bovine brain tubulin in the presence of Zn²⁺ has been studied. Zn²⁺, at concentrations higher than 5 × 10^?5 M caused the formation of sheets, sometimes consisting of up to 50–60 protofilaments oriented in parallel. The sheets were stable towards colchicine, Ca²⁺ and cold treatment. The induction of sheets cannot solely be ascribed to the sulfhydryl blocking properties of Zn²⁺, since other SH reagents (NEM, PCMBS, Cd²⁺ and Hg²⁺) failed to cause similar effects. There are reasons to believe that Zn²⁺ interferes with the closing process of microtubules so that more protofilaments are added in the assembly process than during normal conditions. The system described herein offers a favourable preparation for revealing the ultrastructural organization of microtubules.