Drosophila small cytoplasmic 19S ribonucleoprotein is homologous to the rat multicatalytic proteinase

Abstract

All eukaryotic cells so far analysed contain 19S particles which share a cylinder-like shape and are composed of a set of proteins of relative molecular mass ranging typically from 19,000 to 36,000 (refs 1-10). Proposed functions have included synthetase activity, transfer RNA processing or messenger RNA repression, but their biological importance remains obscure. A multicatalytic proteinase (MCP) of similar size and shape has been isolated from mammalian tissues. The apparent similarities of these high molecular weight complexes suggest a biochemical and functional homology between the small cytoplasmic 19S particle from Drosophila melanogaster (19S-scRNP) (ref. 7) and rat MCP (ref. 14). By means of electron microscopy, immunological techniques, RNA identification and proteinase activity assays, we were able to show that the two structurally similar complexes are immunologically related ribonucleoproteins (RNPs) with similar proteolytic activity.

RNA degrading activity is tightly associated with the multicatalytic proteinase, ingensin

“…Falkenburg et al reported that the rat liver multicatalytic proteinase contains RNA molecules in the size range of 80-100 nucleotides [6]. If the multicatalytic proteinase has RNase activity like prosomes, small RNAs present in the proteinase preparation may be hydrolytic products of the enzyme itself.…”

“…Not only did the purified prosome hydrolyze synthetic peptide substrates and [14C]methylcasein, but antibodies raised against 19S prosome specifically reacted with the multicatalytic proteinase and inhibited its protease activity [6,7]. The prosome is known to be a ubiquitous ribonucleoprotein and was identified as mRNA-protein complexes, including globin and other repressed mRNAs [8,9].…”

Cloning and sequence analysis of a cDNA clone from Arabidopsis thaliana homologous to a proteasome α subunit from Drosophila

“…Proteasomes are multicatalytie complexes consisting of a set of non-identical polypeptides, present in both nuclei and cytoplasm of a variety of eukaryoti¢ c~lls from yeast to man [1][2][3] and also described in archaebaeteria [4], In eukaryot~ these particle~ of a sedimentation eoeffmient of about 20 S have a molecular mass around 700 kDa and constitute about 15=20 different subunits ranging from 21 to 32 kDa [5.-6]. but with different p[ values.…”

Molecular cloning of an essential yeast gene encoding a proteasomal subunit

“…They are composed of multiple subunits (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) which are different in size and charge and which are organised into cylindrical 20 S particles [3][4][5][6]. The proteasome catalyses the cleavage of peptide bonds on the carboxyl side of basic, neutral and acidic residues [7][8][9] but its exact function in the cell is still unknown.…”