Deficiency of nuclease activity in ribosomes of three tumor types

Polysomes isolated from 3 types of neoplasms, mouse mammary adenocarcinoma designated DBAH, morris rat hepatoma 7777, and mouse chloroleukemia, do not undergo fast degradation upon incubation at 37 degrees C, unlike polysomes isolated from corresponding isogenic, normal tissues. Further,. 1M KCl extract of ribosomes from normal cells, in contrast to their neoplastic counterparts, stimulate degradation of poly(U). The nuclease activity in ribosomal preparations from neoplastic cells is not increased in the presence of p-chloromercuribenzoate, a blocking agent of RNAase inhibitor. This suggests that ribosomal preparations from tumor cells are free of nucleases rather than just being masked by an inhibitor. Ribosomes from neoplastic cells stimulate protein synthesis in vitro in the presence of endogenous or exogenous mRNA to a much higher degree than similar preparations from normal tissues. This event is in agreement with the deficiency of nuclease in polysomes from neoplastic cells.