GILLCHRIEST AND BOCK 9 



when it will split, when it is "soluble RNA," and when not. Re-evaluation of 

 Brachet's [26] findings on the relation of ribonucleoprotein to growth phase 

 of yeast will be warranted in the light of current concepts of the importance 

 of buffer media. 



Whereas the divalent cations of the buffer medium play an important role 

 in nucleoprotein structure, there appear to be mineral elements which are in- 

 fluential in nucleic acid function and are not in free equilibrium with the 

 buffer. Zittle [27] and Jungner [28] demonstrated that carefully isolated yeast 

 RNA contained characteristic amounts of metal ions. Kihlman [29] and 

 Mazia [25] have related structural integrity of chromosomes to metal content. 

 Loring and Cooper [30] find that certain cations are important for nucleopro- 

 tein stability of tobacco mosaic virus and hence for infectivity. Racker and 

 Krimsky [31] have evidence that metal ions are involved in an animal virus. 

 These are but a few of the many nucleoprotein-metal systems cited in the 

 literature. 



Thus it appears that for viruses, as well as for subcellular particles, elucida- 

 tion of the structural and functional role of cations will be a fertile and chal- 

 lenging frontier for those with pioneering instincts. 



SUMMARY 



Ribonucleoprotein particles of sedimentation coefficient S 2 o o = S6 have been 

 isolated from A. vinelandii. The particles are free of lipid and DNA. They 

 are stable at neutral pH, in low-ionic-strength solution when divalent cations 

 are present; they are unstable in sucrose, in concentrated salts, and in the 

 presence of ribonuclease. Nucleic acid derived from the particles contains an 

 unidentified fifth base. The 86 S unit reversibly dissociates to particles of 58 

 and 39 S when the Mg ++ concentration is lowered. 



ACKNOWLEDGMENTS 



We are pleased to acknowledge the generous aid of our colleagues. Profes- 

 sor Paul Kaesberg conducted the electron-microscope studies, Miss Vatsala 

 Thakur provided the N-terminal amino acid analyses, and Miss Fay Hoh col- 

 laborated in studies on the protein derived from the particles. Financial support 

 from the National Institutes of Health and Wisconsin Alumni Research Foun- 

 dation is gratefully acknowledged. 



REFERENCES 



1. L. Lilienfeld, Z. physiol. Chem., 18, Ab. A. Claude, Advances in Protein 

 473 (1894). Chem., 5, 423 (1949). 



2. W. Huiskamp, Z. physiol. Chem., 32, 5. W. C. Schneider and G. H. Hoge- 

 145 (1901). boom, /. Biol. Chem. 183, 123 (1950). 



3. R. R. Bensley and N. L. Hoerr, Anat. 6. N. G. Anderson, Science, 121, 775 

 Record, 60, 251 (1934). (1955). 



4a. A. Claude, Harvey Lectures, 43, 121 7. P. Siekevitz and M. L. Watson, /. Bio- 



(1948). phys. Biochem. CytoL, 2, no. 6, 653 (1956). 



