, Volume 237, Issue 1-2, pp 193-205

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

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Monoclonal 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.

We use here the term “prosome” introduced by our laboratory (Schmid et al. 1984) for the then unknown particle and, for its protease activity, use the term “multicatalytic proteinase or MCP” according to the recommendation of the enzymologists concerned (Dahlman et al. 1988; Orlowski and Wilk 1988), in preference to the term “proteasome” suggested by Arrigo et al. (1988)
Communicated by G. Georgiev