GROUP-I METAL-IONS OF INCREASING ATOMIC-WEIGHT SUPPRESS THE GROWTH OFCRYSTALLINE AGGREGATES AND ENHANCE THE GROWTH OF LARGE, SINGLE-CRYSTALS OF T7 RNA-POLYMERASE

Crystals of bacteriophage T7 RNA polymerase gown with ammonium phospha te or ammonium sulfate as precipitant and glycerol as a structure stab ilizing agent exhibit a strong tendency to grow as aggregates. To iden tify an agent that would suppress this behavior a large number of meta l salts were screened as additives to the crystallization solution. Th e singly charged group I metal ions (with the exception of lithium) we re found to suppress the growth of crystalline aggregates and promote the growth of large, single crystals. The degree to which the growth o f aggregates was suppressed and the growth of single crystals was enha nced was clearly and reproducibly correlated with the atomic weight of the metal. Thus, ordered according to their ability to suppress the g rowth of aggregates and enhance the growth of single crystals, the met al ions were Cs > Rb > K > Na.