Fayçal Bey

Phylogenic relationships of the amino acid sequences of prosome (proteasome, MCP) subunits.

Prosomes [or proteasomes, Multi-Catalytic Proteinase (MCP)] are multisubunit protein complexes, found from archaebacteria to man, the structure of which (a 4-layer cylinder) is remarkably conserved. They were first observed as subcomplexes of untranslated mRNP, and then as a multicatalytic proteinase with several proteolytic activities. A number of sequences from subunits of these complexes are now available. Analysis of the sequences shows that these subunits are evolutionarily related, and reveals three highly conserved amino acid stretches. Based on a phylogenic approach, we propose to classify the sequenced subunits into 14 families, which fall into two superfamilies, of the α- and β-type. These data, together with several recently published observations, suggest that some subunits may be interchangeable within the complexes, which would thus constitute a population of heterogenous particles.

The Prosomes (Multicatalytic Proteinases; Proteasomes) and Their Relationship to the Untranslated Messenger Ribonucleoproteins, the Cytoskeleton, and Cell Differentiation†

Publisher Summary This chapter discusses the proteinase function only in relation to the prosome story as a whole and the enzymological mechanisms. Prosomes are “faculative” ribonucleoproteins of about 720,000 M r that display a multicatalytic proteinase activity. Prosomes, called multicatalytic proteinase (MCP) complexes or proteasomes, by many enzymologists, are a new type of cellular factor. They show up in the most varied and unexpected contexts of cellular structure and function, from archeobacteria to humans. They are not only MCPs, with highly selective substrate-specificity, but also a subcomplex of the untranslated messenger ribonucleoprotein (mRNP); they incorporate in a particular state a small ribonucleic acid (RNA) that, in the case of mammalian prosomes, turns out to be a reverse primer of the “retroviral” transfer RNA (tRNA) type. In addition, an important theoretical concept emerges: if the fundamental mechanisms of the mRNA translation are based on ubiquitous factors, the essential differential controls of specific mRNA expression in the cytoplasm are based on a system of mRNA stabilization, acting positively, and of negative controls, by trans-acting factors, exerting their effect on the untranslated mRNA.

The prosomal RNA-binding protein p27K is a member of the α-type human prosomal gene family

SummaryMonoclonal antibodies demonstrated high conservation during evolution of a prosomal protein of Mr 27 000 and differentiation - specific expression of the epitope. More than 90% of the reacting antigen was found as a p27K protein in the free messenger ribonucleoprotein (mRNP) fraction but another protein of Mr 38000, which shared protease fingerprint patterns with the p27K polypeptide, was also labelled in the nuclear and polyribosomal fractions. Sequencing of cDNA recombinant clones encoding the p27/38K protein and comparison with another prosomal protein, p30-33K, demonstrated the existence of a common characteristic sequence pattern containing three highly conserved segments. The genes Hs PROS-27 and Hs PROS-30 were mapped to chromosomes 14 (14g13) and 11 (11p15.1), respectively. The structure of the p27K protein shows multiple potential phosphorylation sites, an NTP-binding fold and an RNA-binding consensus sequence. The Hs PROS-27/β-galactosidase fusion protein binds a single RNA of about 120 nucleotides from total HeLa cell RNA. Sequence comparisons show that the Hs PROS-27 and Hs PROS-30 genes belong to the gene family that encodes the prosome — MCP (multicatalytic proteinase) — proteasome proteins. Comparison with other members of the family from various species allowed us to show that the tripartite consensus sequence characteristic of the α-type sub-family is conserved from archeobacteria to man. The members of this gene family are characterised by very high evolutionary conservation of amino acid sequences of homologous genes and 20%–35 sequence similarity, between different family member within the same species and are clearly distinct from the β-type family.