Purification and characterization of ribosomal proteins from the 30 S subunit of the extreme halophile Halobacterium marismortui.

Ribosomal proteins were extracted from 30 S subunits of Halobacterium marismortui under native conditions.Their separation was based on gel filtration and hydrophobic chromatography, performed at a concentration of 3.2 M KC1 to avoid denaturation. A total of nine proteins were isolated, purified and identified by partial amino-terminal sequences and two-dimension a gel electrophoresis. There is a high degree of sequence homology with 30 S proteins from H. cutirubrum, and also some with 30 (S) proteins of eubacteria.Proton NMR data indicate unfolding of the proteins in low salt. One of the proteins, however, retains its secondary structure at a salt concentration as low as 0.1 M NaCl, and even in 8 M urea. One reason for this outstanding stability could be the high proportion (50%) of ß-structure in this protein as determined from circular dichroism measurements. In general, there is a higher ß-sheet content than for 30 S proteins from Escherichia coli. Measurements of Stokes radii indicate several of the proteins to have a rather elongated shape. One of these is a complex consisting of L3/L4 and L20, similar to the LI-complex from E. co&.The presence of this 50 S complex in the preparation of the small subunit suggests a location on the interface between the subunits.