Production of Mitotic Abnormalities by Ribonuclease.

'Thie nor-mal course of mitosis in plaint anid aniimal cells cali be disrutpted hy miianiy kinids of physical anid chemical agents. Nuclear tranisfoirmations esseiltial to the orderly progress of mitosis can be retarded, chromosome structure deformed, spilndle mechanisms impaired, and cytokinietic processes inhibited. Such disturbaiiees may be revealed, on cytological examinationi of the treated tissues, by a low frequency of dividing cells or a preponderaince of specific stages of mitosis; by the presence of fragmented, adherent, or excessively coiitracted chromosomes; or by the occurrence of aneuploid and polyploid chromosome complexes, tripolar and multipolar spindles, binucleate and multinucleate cells.1 Production of these types of aberrations by a variety of agents suggests that the same cellular constituents are ultimately affected, despite possible differences in the nature of the reaction system initiated by the inciting stimulus. In an effort to identify the structural materials involved, we have determined the capacity of some crystalline enzymes to induce mitotic abnormalities in growing roots of onion and lily. Preliminary experiments revealed that ribonuclease (0.01-0.1 per cent aqueous solutions) induced aberrations of divers types with a high frequency but that equimolar concentrationis of trypsin, chymotrypsin, and deoxyribonuclease had little effeet inl modifying chromosome form and distribution.2 Such differences in cellular response may be due, at least in part, to differences ill ability of these foui enizymes to penietrate the cell; riboumclease has the lowest molecular weight (about 13,000, as (ompared with 20,000-60,000 for the others)3 anid might for that reasoin be expected to enitei the livinig cell more readily. Ani extensive analysis of the actioii of ribonuclease OIn meristematic root-tip cells was accordingly undertaken and forms the basis of the present report. This analysis has led to the conclusion that the production of mitotic alnormalities may be initiated by enzymatic degradation of the riboinucleic acid (ItNA) component of ribonucleoproteins. Experimental Mlethods.-Growing roots of onion (A llium cepa L.) and lily (Lilium tigrinum Ker.) were treated by immersion in aerated solutions of ribonuclease or other reagents that served as controls, for periods ranging from 15 minutes to 48 hours, at room temperature (ca. 220 C.). Seven different samples of ribonuclease were tested,4 and all were effective in inducing mitotic abnormalities. Control solutionis were selected to evaluate the action of the solvents and to determine whether the induced abnormalities could be attributed to properties of the ribonuclease solutions other than their enzymatic activity. Therefore, they included water, potassium phosphate buffer, ribonuclease that had been inactivated by boiling or exposure to ultraviolet radiation, a mixture of amino acids in the proportions characteristic of ribonuclease,5 histone, protamine, egg albumin, sucrose, and a ribonuclease digest of RNA. Cytological diagnosis of the action of the enzyme and