Sadiq Hasnain

Ion effects on protein-nucleic acid interactions: The disassembly of the 50-S ribosomal subunit from the halophilic bacterium, Halobacterium cutirubrum

The 50-S ribosomal subunits from the extreme halophilic bacterium, Halo-bacterium cutirubrum, stable structurally and functionally in concentrated salt solutions were subjected to ionic environments depleted in either K+ or Mg2+ or both. Under these conditions specific classes of proteins are released from the subunit along with the 5 S RNA. Two-dimensional electrophoretic analysis of the resultant split protein fractions indicate some mutually exclusive effects of specific ions on the binding of specific proteins to the 23 S RNA as well as on the retention of 5 S RNA within the ribosomal macrostructure.

Ribosomal protein S1/S1A in bacteria.

Recently, Escherichia coli ribosomal protein Sl has been shown to have important and diverse functions in the logistics of mRNA processing during in vitro protein synthesis [l-9] and Qfl replication [lo-121. In the course of an RNA-protein interaction study with Sl, we discovered that there are two distinct large molecular weight ribosomal proteins, both of which have been designated as Sl by different laboratories. The two proteins have been purified, characterized, and designated as Sl and Sl A. In view of the functions ascribed to Sl in the interaction with mRNA [l-9] , 16 S RNA [13] and other proteins (a replicase) [ 11,141, the question naturally arises as to the universality of the Sl type protein in various organisms. Indeed, it has been stated that certain specialized bacterial types lack

Temperature related alterations in the acidic alanine-rich "A" protein from the 50S ribosomal particle of the extreme halophile, Halobacterium cutirubrum.

Summary50-S ribosomal subunits from the extreme halophilic bacterium, Halobacterium cutirubrum, contain an alanine-rich acidic “A” protein which resembles the L7-L12 multimer (Kaltschmidt and Wittmann, 1970) found in the 50-S ribosomal subunit of Escherichia coli cells. The protein contains 24 mole % alanine and is devoid of histidine, tryptophan and cysteine. Unlike E. coli which has two forms of the “A” protein distinguished solely by the acetylation state of the serine amino terminus. H. cutirubrum 50-S subunits contain only one unsubstituted form of the “A” protein in vivo. However, during purification of ribosomes from cells grown between 25 and 37°C the latter “A” protein undergoes rapid, specific, in vitro enzymatic alteration at its carboxy-terminal end. When the halophile is grown in the temperature range of 40 to 42°C the cleaving enzyme is not active and only one form of the “A” protein is found on the ribosomes.