Studies on the structure of rat-liver polysomes by small-angle X-ray scattering

The spatial structure of rat liver polysomes in dilute solution has been studied by the small-angle X-ray scattering technique. The distance between the mass centres of neighbouring ribosomes on the mRNA molecule is 35 nm, and the distance from next-but-one neighbour, about 55 nm. The spatial arrangement of the ribosomes on the polysome is compact; stretched configurations can be ruled out. The best model is a solenoid with six ribosomes per turn and a pitch of about 33 nm. The greatest diameter of a polysome with eight ribosomes is 130 nm, the radius of gyration 34 nm.