IDENTIFICATION AND INITIAL CHARACTERIZATION OF A SPECIFIC PROTEASOME (PROSOME) ASSOCIATED RNASE ACTIVITY

We have identified and characterized a specific nuclease activity to b e tightly associated with proteasomes. Using tobacco mosaic virus RNA (TMV-RNA) as substrate to analyze and quantify the cleavage reaction, we supply several lines of evidence that this nuclease activity is an integral part of proteasomes. Thus, RNase activity was coincident with the elution profiles of proteasomes at each stage of purification. Pr oteasomal nuclease activity was resistant to strong dissociation condi tions using 480 mM KCl, 0.5% sodium lauroylsarcosinate, and 6 M urea. This nuclease activity remained associated with an urea-resistant subc omplex of the proteasome comprising a specific set of proteins. Finall y the digestion of TMV-RNA led to a well defined pattern of RNA fragme nts while 5 S ribosomal RNA and globin mRNA were not degraded. These r esults provide further evidence that proteasomes are able to discrimin ate between different RNAs, and the possible involvement of proteasome s in translation control is discussed.