lyo SUBCELLULAR PARTICLES 



31. LlTTLEMhl.D, J. W., R. B. KlLLKR, J. GrOSS AND P. C. ZaMECMK. /. Biol. CllCm. llj: III, 



1955- 



32. LoFTFiELD, R. B. I'rogr. ill Biophys. Biophyi. Chcni. M: 347, 1957. 



33. Palade, G. E. and p. Siekevitz. /. Biophys. Biochcm. Cytol. 2: 171, 1956. 



34. ScHWEET, R. S., F. C. BovARD, E. Allen and E. Glassman. Pioc. Nut. Acad. Sci. 44: 173, 

 1958. 



35. SiEKEvnz, F. /. Bivl. Chcin. 195: 549, 1952. 



36. SiMKiN, ]. L. AND T. S. Work. Biochem. }. 65: 307, 1957. 



37. Strittmatter, C. F. and E. G. Ball. Pioc. Nut. Acad. Sci. 38: 19, 1952. 



38. Symposium — Amino Acid Activation. Proc. Nat. Acad. Sci. 44: 67, 1958. 



39. Webster, G. C. /. Biol. Chein. 229, 535, 1957. 



40. Weiss, S. B., G. Acs and F. LIP^L\NN. Fed. Pioc. 17: ^^i, 1958. 



41. Weiss, S. B., G. Acs and F. Lipmann. Pioc. Nat. Acad. Sci. 44: 189, 1958. 



42. WiNNicK, T., F. Friedberg and D. M. Greenberg. Arch. Biochem. 15: 160, 1947. 



43. Zamecnik, p. C. and E. B. Keller. /. Biol. Chem. 209: 337, 1954. 



44. Zamecnik, P. C, M. L. Stephenson and L. I. Hecht. Pioc Nat. Acad. Sci. 44: 73, 1958. 



45. Zamecnik, P. C., M. L. Stephenson, }. F. Sc:ott and M. B. Hoagland. Fed. Proc. 16: 



275< 1957- 



DISCUSSION 



E. L. Kuff, M. L. Stephenson, R. A. Lewin, J. Roth, R. E. Beyer, 



A. Marshak, R. Milkman 



Dr. Kuff: Is there any evidence for the incorporation of soluble RNA into the 

 microsomal nucleoprotein concomitant with the incorporation of amino acid? 



Dr. Stephenson: Dr. Hoagland has labeled S-RNA //; vivo using C'^-orotic acid. 

 This pyrimidine-labeled S-RNA was isolated and was incubated with non-labeled 

 microsomes, soluble enzymes and ATP. The microsomes were subsequently reisolated. 

 Some radioactivity was found in the microsomal RNA and this labeling was enhanced 

 by GTP. These findings are under study now. (Stephenson, M. L., P. C. Zamecnik 

 AND M. B. Hoagland. Fed. Proc. 18: 331, 1959.) 



Dr. Lewin: The observation that the incorporation of different amino acids is addi- 

 tive may be evidence for heterogeneity in the soluble RNA. Have attempts been made 

 to separate RNA fractions which might be specific for different amino acids? 



Dr. Stephenson: No real attempts have been made to fractionate S-RNA in our 

 laboratory. I understand that this is being done in other laboratories with preliminary 

 indications that there are several specific RNA molecules. 



Dr. Roth: Have you any evidence as to whether the labeled amino acids which are 

 incorporated into the soluble RNA in the supernatant fraction are located at the ends 

 of the chain or randomly along the chain? You know that the nucleotides are incor- 

 porated at the ends, for example. 



Dr. Stephenson: Because the binding of all amino acids to S-RNA and the incor- 

 poration of the terminal adenine residue into S-RNA are both dependent upon the 

 presence of CTP, the amino acid is very likely attached to the end group of S-RNA. 

 The 2' or 3' hydroxyl of the terminal ribose of S-RNA could be the binding site, 

 especially since Dr. Lipmann and Dr. Weiss have reported finding an ATP-amino acid 



