Topography and stoichiometry of acidic proteins in large ribosomal subunits from Artemia salina as determined by crosslinking.

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Abstract
The 60S subunits isolated from Artemia salina ribosomes were treated with the crosslinking reagent 2-iminothiolane under mild conditions. Proteins were extracted and fractions containing crosslinked acidic proteins were obtained by stepwise elution from CM-cellulose. Each fraction was analyzed by "diagonal" (two-dimensional nonreducing-reducing) NaDodSO4/polyacrylamide gel electrophoresis. Crosslinked proteins below the diagonal were radioiodinated and identified by two-dimensional acidic urea-NaDodSO4 gel electrophoresis. Each of the acidic proteins P1 and P2 was crosslinked individually to the same third protein, P0. The fractions containing acidic proteins were also analyzed by two-dimensional nonequilibrium isoelectric focusing-NaDodSO4/polyacrylamide gel electrophoresis. Two crosslinked complexes were observed that coincide in isoelectric positions with monomeric P1 and P2, respectively. Both P1 and P2 appear to form crosslinked homodimers. These results suggest the presence in the 60S subunit of (P1)2 and (P2)2 dimers, each of which is anchored to P0. Protein P0 appears to play the same role as L10 in Escherichia coli ribosomes and may form a pentameric complex with the two dimers in the 60S subunits.