[Nuclear ribonucleoprotein particles containing messenger RNA. 12. Studies of dissociation and reconstruction of 30S particles].

Protein of purified 30S particles analyzed by sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis is present mainly as two bands with the apparent molecular weight of 38 000 and 41 000 daltons. These bands contain not less than 90% of the total protein. When the same material is electrophoresed in the presence of urea (pH 4.5) it migrates as one homogeneous band. The procedure for isolation of free informofers in preparative scale is described. The free informofers do not contain rapidly labeled RNA and are not stable: they dissociate reversibly into protein subunits of lower molecular weights. The dissociation is concentration dependent: low concentration of protein facilitates the dissociation process. Both whole informofers and their protein subunits easily interact with free pro-mRNA yielding 30S RNP. However only the product of reconstruction with informofers is similar to native 30S particles, according to several biochemical tests. These data support the model of the structure of nuclear RNP particles according to which pro-mRNA is distributed on the surface of globular protein particles.