An electrophoretically silent polymorphism for the beta chains of rabbit hemoglobin and associated polyribosome patterns

The β chain of rabbit (Oryctolagus caniculus) hemoglobin has previously been reported to contain a single residue of isoleucine at β¹¹². The authors detected other rabbits with either zero isoleucyl residues or half a residue per β chain. This character is polymorphic and inherited as a simple mendelian autosomal codominant. Normally the modal number of ribosomes per polyribosome is 4 to 6 in reticulocyte lysates; but incubation of rabbit reticulocytes prior to lysis with L-o-methylthreonine (OMT), an isostere of isoleucine, leads to a bimodal distribution in lysates with 2 to 3 and 8 to 12 ribosomes as modes. This alteration has been attributed to ribosomal traffic jams caused by starvation for ile-tRNA at mRNA codons corresponding to the locations of isoleucyl residues at position α¹⁰, α¹⁷, α⁵⁵ and β¹¹². The authors confirmed this interpretation by incubating OMT with reticulocytes from rabbits with integral, half integral and nil values for isoleucyl residues per β chain to show that formation of the larger clusters of polyribosomes requires that β¹¹²=ile.