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Physicochemical and Metabolic Studies on 

 Rat Liver Ribonucleoprotein 1 



MARY L. PETERMANN MARY G. HAMILTON 



M. EARL BALIS KUMUD SAMARTH - PAULINE PECORA 



Sloan-Kettering Institute for Cancer Research 

 and Sloan-Kettering Division, Cornell University Medical College 



The presence in uninfected tissues of particles with sedimentation constants 

 of about 75 S has long been known to virologists [1]. Similar macromolecules 

 have been found in tumors (Kahler and Bryan [2]). We first observed them 

 in spleen [3], and later in liver, pancreas, and various tumors [4]. They are 

 now known to be ribonucleoproteins (RNP) [5]. Ultracentrifugal patterns of 

 these RNPs show a number of boundaries. Their sedimentation coefficients 

 are so strongly dependent on concentration that we have denoted them by 

 letters, such as B, C, and E, rather than identifying them by their sedimenta- 

 tion constants at infinite dilution. B has a sedimentation constant of 78 S, C of 

 about 62 S, and E of 46 S, corresponding roughly with the S80, S60, and S40 

 boundaries found in nucleoproteins from microorganisms. 



In general, where we find a large amount of nucleoprotein B, as in pancreas 

 and normal liver [4], the electron microscopists find most of the granules at- 

 tached to endoplasmic reticulum [6] ; but where we find increased amounts of 

 C and E, as in liver tumors [4], the electron microscopists find granules not 

 attached to reticulum [7]. We therefore wanted to see whether a large micro- 

 some fraction, containing only RNP bound to endoplasmic reticulum, con- 

 tained only B, while a small microsome or ultramicrosome fraction containing 

 free RNP particles was rich in C and E. 



1 The authors wish to acknowledge the assistance of the Atomic Energy Commission 

 (Contract no. AT (30-1)— 910), and the National Cancer Institute of the United States 

 Public Health Service (grants nos. C-2329 and CY-3190). 



2 Visiting research fellow. 



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