[Discovery of "masked" ribonucleases in highly purified preparations of RNA]

It was found that RNA preparations isolated with the help of various inhibitors of RNAses from different eukariotic tissues, followed by thorough deproteinization contain particular ribonucleases ("masked" RNAses). These RNAses were supposed to be connected with RNA molecules and are not active. They may be activated by changes of RNA molecule conformation. Apparently the "marked" RNAses can take part in (a) processing of large precursor RNA molecules; (b) regulation of gene expression by means of specially cut RNA fragments.