Differences in the Structural Organisation of the Two Subunits of Escherichiα coli Ribosome

Molecular Biology Unit, Department of Biochemistry, Institute of Medical Sciences,
Banaras Hindu University, Varanasi-221 005, U. P.

Various approaches that are being made in our and other laboratories to understand the overall structural organisation of the complex organelle, the 70S ribosome and its subunits 50S and 30S ribosomes, have been reviewed. lmmuneelectron microscopy and neutron diffraction analysis are two of the most sophisticated techniques being employed and considerable amount of information bas already been obtained with the help or these two techniques. In oar laboratory simpler approaches are being made towards the understanding or the differences in the structural organisation of the two subunits. These include: (1) kinetics of degradation of ribosomes and their subunits by RNasel and the inhibitory capacity of the 70S and 30S ribosomes towards the RNasel eatalysed hydrolysis of polyribonucleotides, (l) the binding of the intercalating and noninterealating dyes to the ribosomes, (3) the differeatial effects of formaldehyde on the two subunits, (4) differential effects of putrescine and spermidine on the subunits, (5) differences in the action of trypsin and (6) immuno precipitation or ribosomes and their subunits. These investigations clearly point out  that the structure or 30S ribosome is less flexible than that of 50S ribosome ; further, the 50S ribosome has an RNA-rich and protein-poor region which is most likely to be the 'L7/Ll'12' stalk visualised by Lake and his coworkers by immuneelectron microscropy. This stalk may have au important functional role to play.