Polysomes protease activity

In a sensitive, solid-phase assay for endo-proteases (27, 54), the activity of polysomes and monosomes were compared. Shown in Table 1 is the loss of activity of SOS ribosomes from infected cells, but the retention of activity on polysomes. This data suggests continuing participation of a polysomal protease activity in viral... 

Recent evidence points to the presence of protease activity-associated with polysomes and ribosomes when extracts of uninfected cells are assayed (refs. 27 32, Figure j). Characteristic of infection of cells by poliovirus is drastic, rapid inhibition of protein synthesis. Poliovirus infection also depresses the ribosomal protease activity (27, 29, 55) Ribosomes from uninfected cells have been reported to possess an autoproteolytic activity (31, 32), and this has been confiimed by two-dimensional gel analysis (Figure 4) Poliovirus infection of HeLa cells reduces the autoproteolysis of isolated 808 ribosomes markedly (not shown). The inhibition of HeLa cell ribosomal protease activity requires protein synthesis, but proceeds in the presence of guanidine (55) ... 

Later experiments provided the initial evidence to suggest that the synthetic passivity of the ribosomes of unfertilized oocytes could be due to absence of interaction between templates of protein synthesis and mRNA molecules, or to the presence of too few templates, as a result of which the ribosomes were uncharged and did not form polysomes (Nemer, 1962 Wilt and Hultin, 1962 Nemer and Bard, 1963 Hultin, 1964). When synthetic systems were created in vitro and mRNA molecules were replaced by synthetic polynucleotides, no significant differences were found between the ribosomes of fertilized and unfertilized oocytes. It was soon shown, however, that the messenger RNA synthesized during oogenesis can combine with ribosomes, but cannot exercise its functions because of special protein membranes, which evidently break up during activation of the oocytes as a result of increased protease activity (Monroy et al., 1965). 

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