Heterogeneity of the native ribosomal subunit fraction in HeLa cells

The cytoplasm of growing HeLa cells contains a certain quantity of native ribosomal subunits. They constitute a heterogeneous fraction consisting of at least two categories of particles. The first category comprises the newly emerging native 40S subunits which do not form 80S couples under any in vitro condition tried. It is postulated that these native subunits carry an anti-association factor which cannot be stripped off by 0.5 м KCl treatment. Transiently native subunits of the second category reassociate to 80S ribsomes only in the presence of an association factor.