Proteasome‐associated RNAs are non‐specific

Abstract

The RNA isolated from RNase-treated proteasome preparations from human erythrocytes, HeLa cells, the archaeon Thermoplasma acidophilum and also from recombinant proteasomes of T acidophilum expressed in Escherichia coli was characterized. The RNA associated with structurally similar protein particles, namely with the two molecular chaperones, groEL from E. coli and with the thermosome from ir: acidophilum, served as controls. Electrophoretic analysis on polyacrylamide gels of the radioactively end-labelled RNA revealed a very similar size distribution pattern, irrespectively of the protein particles from which they had been isolated. The predominant RNA species were in the size ranges 80 nucleotides and 120 nucleotides, respectively. Partial sequencing of their terminal regions by mobility-shift analysis revealed that, of the proteasomes from human erythrocytes, the approximately 80-nucleotide-long RNA consists of a heterogenous population of mostly tRNA species because they carried the tRNA-specific 3'-terminal sequence motif 5'-CCA-3'. The RNA in the size range 120 nucleotides isolated from the proteasomes of human erythrocytes and of T. acidophilum was also heterogeneous and displayed, in the terminal regions, a remarkable sequence similarity to the corresponding regions of the 5s rRNA from the same and different organisms. The total content of RNA of all the protein particles was quantified and found to be consistently sub-stoichiometric. All these findings strongly suggest that RNA associated with the proteasomes and with the molecular chaperones originate from the abundant cellular pool of the tRNAs and 5s rRNAs which bind non-specifically to these large protein particles.

Possible Involvement of Proteasomes (Prosomes) in AUUUA-mediated mRNA Decay

“…We found that a minimum of two AUUUA motifs is required for the destabilization by proteasomes. We detected only one cleavage site with (AUUUA) 2 oligo-RNA, whereas incubation of (AUUUA) 4 oligo-RNA with proteasomes produced five fragments corresponding to five cleavage sites (Fig. 6).…”

“…eration of degradation of ARE containing messengers. Others described a 32-kDa protein identical to HuR that specifically cross-links to (AUUUA) 4 and (AUUUUA) 3 but not (AUA) 8 and (AUUA) 5 RNAs in vitro (30). This protein would play an RNAstabilizing role in the ARE-directed mRNA decay in mammalian cells (31).…”

“…The RNA content depends on the origin of the proteasomes and decreases with increasing proteasome purity (4,5). These RNAs are heterogeneous in size but migrate most frequently in a molecular size range of 70 -200 nucleotides (5).…”

Regulation of apoptosis by the ubiquitin and proteasome pathway

“…Independently on their study as proteolytic enzymes, proteasomes have also been described as "prosomes" which formed ribonucleoprotein complexes and were supposed to regulate mRNA distribution in cells [25,46]. It now seems, that the association of mRNA with proteasomes is rather a bystanding phenomenon without major significance [47].…”

“…It now seems, that the association of mRNA with proteasomes is rather a bystanding phenomenon without major significance [47].…”