GILLCHR1EST AND BOCK 



Fig. 3. An electron micrograph of a central portion of a sprayed droplet showing RNP 

 particles magnified 170,000 times. The smallest particles are about 200 A in diameter, the 

 largest about 250 A. From the shapes of their shadows it is estimated that their thicknesses 

 are about 75 per cent as great as their diameters. Taken on a Siemens Elmiskop I by 

 Professor Paul Kaesberg. 



are electron micrographs of a purified preparation of the 86 S particles which 

 was diluted lOOOfold with distilled water and then quickly sprayed on a col- 

 lodion membrane and air-dried. It is not yet known how the short exposure to 

 distilled water will affect particle structure. The electron micrographs taken 

 under these conditions show that at least two size classes are present, both of 

 which are roughly spherical. The 86, 58, and 39 S particles all show small de- 

 pendence of sedimentation coefficient on concentration, which also suggests 

 that the particles are not markedly asymmetric. 



The particles appear to contain ribonucleic acid and protein and to be free 

 of lipid and deoxy nucleic acid. The nucleic acid component has been sepa- 

 rated and purified by detergent treatment [17], phenol [18], chloroform [19], 

 and glacial acetic acid [20] extraction. The protein component when sepa- 

 rated from the nucleic acid has been found to be insoluble in aqueous solutions 

 unless prepared through a 67 per cent glacial acetic acid procedure. The pro- 

 tein shows an ultraviolet absorption typical of a protein rich in tyrosine. We 

 have derived only one major protein from the particle at this point. The de- 

 rived protein appears to have only one type of N-terminal amino acid, which 

 we have very tentatively identified as glycine. The number of protein subunits 

 per particle has not yet been quantitatively determined, but the experiments to 

 date suggest a large number. 



