viii MICROSOMAL PARTICLES 



been proved guilty beyond all reasonable doubt. In the last few years, however, 

 there have been marked advances in the study of the particles which promise 

 to resolve these lingering doubts. Thus a symposium dealing with the particles 

 and their function in living cells could hardly fail to bring forth new and 

 exciting information. 



In this symposium a number of papers were concerned with methods of 

 isolation, the size, the composition, and the stability of the particles. One strik- 

 ing observation was that particles of roughly 80 S are found in a wide variety 

 of materials; another area of agreement was in the requirement for magnesium 

 to stabilize the particles. There was a consensus of opinion that carefully puri- 

 fied particles have little enzymatic activity and that their RNA content is 40 

 per cent or more. Several reports showed that the protein moieties of nucleo- 

 protein have certain distinctive properties. Other studies explored the reasons 

 for the variations in particle sizes that are observed both in vivo and in vitro. 

 New kinetic data were presented which indicate that the protein of the par- 

 ticles does not serve as precursor material for nonparticulate protein. The in- 

 corporation of adenylamino acids was demonstrated in one study which also 

 illuminated the need for caution in the interpretation of incorporation studies. 

 Other papers reported less direct methods of approach to the understanding of 

 the particles and their role in protein synthesis, such as studies of radiation 

 effects and studies of incorporation of amino acid analogs. All together these 

 reports provide a number of new facts that must be taken into account by any 

 theory of protein and nucleic acid synthesis. 



During the course of the symposium a semantic difficulty became apparent. 

 To some of the participants, microsomes mean the ribonucleoprotein particles 

 of the microsome fraction contaminated by other protein and lipid material; 

 to others, the microsomes consist of protein and lipid contaminated by particles. 

 The phrase "microsomal particles" does not seem adequate, and "ribonucleo- 

 protein particles of the microsome fraction" is much too awkward. During the 

 meeting the word "ribosome" was suggested; this seems a very satisfactory 

 name, and it has a pleasant sound. The present confusion would be eliminated 

 if "ribosome" were adopted to designate ribonucleoprotein particles in the size 

 range 20 to 100 S. 



The symposium provided to the participants an opportunity for comparing 

 notes on methods and techniques and for exchange of views on the status of 

 various problems. It undoubtedly affected the immediate research plans of a 

 number of the participants. This volume is being published in the hope that 

 it will extend some of these benefits to those who did not attend. 



