The relationship between reticulocyte polyribosome structure and function

Abstract

The relationship between the morphologic structure of reticulocyte polyribosomes and their function in protein synthesis has been investigated. When reticulocyte polyribosomes are maintained at 37° in 1.5·10 −3 M MgCl 2 at pH 7·4 during the first 7 h only 15% of the polyribosomes are broken down to smaller units, but not to soluble nucleotides or small chain polynucleotides. During this time, however, 70% of the capacity to synthesize protein is lost. This decrease cannot be corrected by the addition of an energy-generating system or soluble supernatant factors. 4 M urea and 1·10 −3 M p-chloromercuribenzoate (PCMB) break down reticulocyte polyribosomes, with loss of function, to units of 80 S or smaller. This morphologic effect is reversible upon removal of the reagents, but full return of polyribosome function in protein synthesis does not occur. It is concluded that: (1) ribonuclease is not an inherent part of the reticulocyte polyribosome, (2) alterations in the ribosomal proteins induced by PCMB and urea cause disaggregation of reticulocyte polyribosomes, (3) the presence of messenger RNA on reticulocyte ribosomes does not confer protection against the action of erythroid cell ribonuclease, and (4) the factors which are responsible for maintaining polyribosome aggregation in the reticulocytes are not totally identical with those which are necessary to insure optimal function in protein synthesis.