Specific ribonucleoprotein fragments from 40-S ribosomal subunits

The anomalous migration during two-dimensional gel electrophoresis of eukaryotic ribosomal proteins with oxidised thiol groups

Two-dimensional gel electrophoresis of eukaryotic ribosomal proteins under conditions in which thiol groups are not maintained in a reduced state has been found to cause marked changes in the migration of certain proteins, apparently due to the formation of intramolecular disulphide bridges. The results suggest that certain previously designated eukaryotic ribosomal proteins are not, in fact, unique species.

Reductive alkylation of mammalian ribosomes

40- and 60-S ribosomal subunits and 80-S ribosomes from rat liver were highly labelled by reductive methylation using formaldehyde and sodium boro-[3H] hydride, under conditions which did not decrease their activity in poly-U-directed polyphenylalanine synthesis. Dissociation of the monosomes, subunits dimers, and polysomes into free subunits was observed after methylation. Free proteins labelled after extraction from the ribosomal subunits incorporated 7 times more radioactivity than when labelled in the subunits. Proteins extracted from methylated subunits and ribosomes were analyzed by two-dimensional gel electrophoresis, and the radioactivity of each protein was compared to that of the same free protein. A classification of the proteins was established according to their accessibility to the reagents in the subunits and the ribosomes.

Effect of ribonuclease T1 on ribosomal subunits of rat liver

The accessibility of 28S RNA within the ribosomal subunits to ribonuclease T1 was studied, in comparing results obtained after enzyme treatment of compact, K+ deficient 60S subunits and of EDTA-treated 60S subunits. RNA, extracted from the subunits, using a mixture of sodium dodecyl sulfate and phenol was analyzed on sucrose gradients. The RNA from active subunits was only degraded in high enzyme concentrations. In the K+ deficient subunits, RNA is more accessible since it breaks down into 6 well-defined fragments, sedimenting between 4S and 18.5S. Within the EDTA-subunits, there is no more protection of the RNA. In fact, it is degraded by weak enzyme concentrations, as is the free 28S RNA, giving heterogeneous fragments. Comparison of the melting curves of subunits and free 28S RNA showed that it is only in EDTA subunits that proteins do not stabilize the secondary structure of RNA. In the case of 40S subunits, the action of ribonuclease T1 combines with the action of the endogenous nuclease which makes the degradation process more difficult to analyze.