McCLURE AND ROBERTS 



155 



suits were erratic from one preparation to another, and the incorporation rate 

 was only 1/1000 that of intact cells at the highest. Accordingly contamination 

 by intact cells was a constant worry. The number of intact cells was estimated 

 both by plate counts and by microscopic examination. The uptake observed 

 was as much as 100 times that which could be attributed to the contaminants. 



There were also several qualitative features which distinguish the behavior 

 of the protomorph preparation from that of intact cells. In the first place, the 

 incorporation doubled if ATP was added or if the concentration of the amino 

 acid mixture was doubled. These variations have little effect on incorporation 

 by whole cells. Secondly, the distribution of incorporated radioactivity among 

 the fractions soluble in cold TCA, alcohol, ether, and hot TCA was different 

 from that obtained with whole cells [3]. Finally, the hot-TCA-insoluble ma- 

 terial after hydrolysis yielded a pattern of radioactive amino acids different 

 from the mixture supplied and different from what would be incorporated by 

 whole cells. 



Accordingly we believe that the observed incorporation was in fact real, 

 though not reproducible from day to day. Since these experiments were done 

 we have learned of the activity of the cell-wall fraction in protein synthesis 

 [7, 8]. In retrospect it seems quite likely that the variability in the synthetic 

 capacity of the protomorphs may have been due to a variability in their content 

 of cell-wall fragments. 



These protomorphs are of course very different from the ribosomes which 

 are the subject of this symposium, but there may be a relationship between 

 them. It is a common belief that the bacterial cell is not a homogeneous mix- 

 ture of its various components; on the contrary, various lines of evidence indi- 

 cate that it has a high degree of organization. Organization in turn implies 

 the action of forces between the various constituents such as DNA, RNA, pro- 

 tein, and ribosomes. It is possible that the aggregation of these cellular con- 

 stituents into protomorphs may be another manifestation of the same forces 

 which maintain organization in the living cell and may furnish a material in 

 which the forces are more amenable to study. If so, the protomorphs may 

 eventually contribute to our knowledge of how the ribosomes are organized 

 within the cell. 



REFERENCES 



1. S. Spiegelman, A Symposium on the 

 Chemical Basis of Heredity, p. 232, Johns 

 Hopkins Press, 1957. 



2. B. Nisman, personal communication, 

 1957. 



3. R. B. Roberts, P. H. Abelson, D. B. 

 Cowie, E. T. Bolton, and R. J. Britten, 

 Studies of Biosynthesis in Escherichia coli, 

 Carnegie Inst. Wash. Publ. 607, 1955. 



4. E. T. Bolton, B. H. Hoyer, and D. B. 

 Ritter, paper 3 of this volume. 



5. Z. Dische, The Nucleic Acids, vol. I, 

 chapter 9, Academic Press, New York, 

 1955. 



6. O. H. Lowry, N. J. Rosebrough, A. L. 

 Farr, and R. J. Randall, /. Biol. Chem., 

 193, 265 (1951). 



7. V. R. Srinivasan and S. Spiegelman, 

 Bacterial. Proc, 58, 101 (1958). 



8. S. Ochoa, Spring Meeting, National 

 Academy of Sciences, 1958. 



