Stoichiometric measurements of 30S and 50S ribosomal proteins from Escherichia coli.

Abstract

Stoichiometric investigations were made for all 21 proteins of the 30S subunit and for 31 proteins of the 50S subunit. While the results for the 30S proteins strongly suggest the existence of two different stoichiometric classes, the so-called “fractional” (F) and “unit” (U) proteins with average molar amounts of 0.1–0.5 and 0.8–1.2 per mole 30S respectively, at least one further group is present in isolated 50S particles. Therefore 50S proteins may be subdivided in the following way: a) 9–10 proteins with average molar amounts of 0.2–0.6 (F-proteins), b) 15–16 proteins with 0.8–1.2 copies per 50S particle (U-proteins), c) at least one protein with an average value of 1.8–2.2 copies, the “repeated” (R) proteins, d) a group of 7 proteins with 1.4–1.7 copies per particle; they can be named “fractional repeated” (FR) proteins. These findings indicate that 50S ribosomal particles show a more differentiated degree of structural heterogeneity at least in vitro than has been shown for 30S subunits.