The Ribosomal Proteins of L Cells

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Abstract
To approach the problem of the RNA‐protein and protein‐protein non‐covalent interactions in mammalian ribosomes, the behaviour of the ribosomal proteins of L cells has been studied under various conditions. Firstly the electrophoretic patterns of the ribosomal proteins extracted from KCl‐washed subunits dissociated by EDTA or puromycim have been compared. All the ribosomal proteins of the EDTA‐derived subunits are found on the puromycin‐derived subunits with the exception of two (S20, S22) not observed when puromycin is used to dissociate the subunits. Three polypeptides of the puromycin‐derived subunit, SP0, LP1, LP3, are stripped by the sole removal of Mg2+ when EDTA is used. Other additional polypeptides are found on the KC1‐washed puromycin‐derived subunits. Secondly, the dissociating effect of 0.5 M KCl on the proteins of the subunits dissociated by EDTA or puromycin has been studied. Although the EDTA‐derived subunits appear much more sensitive to KCl, nevertheless 0.5 M KCl also releases ribosomal proteins from the puromycin‐derived subunits. Other polypeptides (core proteins) are not susceptible to KCl split off. Thirdly, some ribosomal proteins are able to transfer from one type of subunit to the other; these proteins have been classified into three groups. Although the deprivation of Mg2+ enhances this phenomenon, seven pairs of putative transferable proteins are observed in subunits dissociated both by EDTA and puromycin. Lastly, a comparative study has been made between the proteins split off by KCl, the core proteins and the transferable proteins with the ribosomal polypeptides labelled in the absence of rRNA synthesis. A correlation has been observed between the proteins split off by KCI, the transferable proteins and the labelled proteins; however, none of the core proteins are transferable and the major part of them remain unlabelled. This study suggests that the transfer, splitting of and labeling of proteins are properties related to the topological location of the proteins in the ribosomal structure.