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Importin/karyopherin protein family members required for mRNA export from the nucleus.

ABSTRACT: The yeast Saccharomyces cerevisiae contains three proteins (Kap104p, Pse1p, and Kap123p) that share similarity to the 95-kDa beta subunit of the nuclear transport factor importin (also termed karyopherin and encoded by KAP95/RSL1 in yeast). Proteins that contain nuclear localization sequences are recognized in the cytoplasm and delivered to the nucleus by the heterodimeric importin complex. A second importin-related protein, transportin, delivers a subset of heterogeneous nuclear ribonucleoproteins (hnRNPs) to the nucleoplasm. We now show that in contrast to loss of importin beta (Kap95p/Rsl1p) and transportin (Kap104p), conditional loss of Pse1p in a strain lacking Kap123p results in a specific block of mRNA export from the nucleus. Overexpression of Sxm1p, a protein related to Cse1p in yeast and to the human cellular apoptosis susceptibility protein, relieves the defects of cells lacking Pse1p and Kap123p. Thus, a major role of Pse1p, Kap123p, and Sxm1p may be nuclear export rather than import, suggesting a symmetrical relationship between these processes.

SUBMITTER: Seedorf M

PROVIDER: S-EPMC23031 | biostudies-literature | 1997 Aug

REPOSITORIES: biostudies-literature

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Importin/karyopherin protein family members required for mRNA export from the nucleus.

Seedorf M M Silver P A PA

Proceedings of the National Academy of Sciences of the United States of America 19970801 16

The yeast Saccharomyces cerevisiae contains three proteins (Kap104p, Pse1p, and Kap123p) that share similarity to the 95-kDa beta subunit of the nuclear transport factor importin (also termed karyopherin and encoded by KAP95/RSL1 in yeast). Proteins that contain nuclear localization sequences are recognized in the cytoplasm and delivered to the nucleus by the heterodimeric importin complex. A second importin-related protein, transportin, delivers a subset of heterogeneous nuclear ribonucleoprote ...[more]

PMID: 9238021

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Project description:BACKGROUND: Malaria caused by protozoan parasites of the genus Plasmodium spp. is a major health burden in tropical countries. The development of new control tools, including vaccines and drugs, is urgently needed. The availability of genome sequences from several malaria parasite species provides a basis on which to identify new potential intervention targets. Database mining for orthologs to the Plasmodium falciparum trophozoite protein R45, a vaccine candidate, led us identify a new gene family. RESULTS: Orthologs to the P. falciparum trophozoite protein R45 were detected exclusively in protozoan parasites of the phylum Apicomplexa, including several Plasmodium spp., Toxoplasma gondii and Cryptosporidium parvum. All family members are hybrid genes with a conserved C-terminal protein kinase domain of a novel type, recently called FIKK kinase, associated with a non conserved N-terminal region without any known functional signature. While a single copy gene was detected in most species, considerable gene expansion was observed in P. falciparum and its closest phylogenic relative P. reichenowi, with 20 and six copies, respectively, each with a distinct N-terminal domain. Based on full length protein sequence, pairs of orthologs were observed in closely related species, such as P. berghei and P.y. yoelii, P. vivax and P. knowlesi, or P. reichenowi and P. falciparum. All 20 P. falciparum paralogs possess a canonical Plasmodium export element downstream of a signal / anchor sequence required for exportation outside the parasitophorous vacuole. This is consistent with the reported association of the trophozoite protein R45, the only paralog characterised to date, with the infected red blood cell membrane. Interestingly, most genes are located in the subtelomeric region of chromosomes, in association with other multigene families contributing to the remodelling of the infected red blood cell membrane, in particular the ring erythrocyte surface antigen multigene family. CONCLUSION: This Apicomplexan-specific gene family was called R45-FIKK kinase. The family hallmark is a kinase domain with unusual characteristics, raising the possibility of designing drug or vaccine strategies targeting this domain. The characteristics of the P. falciparum family suggest a role in remodelling the infected cell and as such possibly contribute to the particular virulence of this species.

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Importin/karyopherin protein family members required for mRNA export from the nucleus.

Publications

Importin/karyopherin protein family members required for mRNA export from the nucleus.

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