Maize ribosome-inactivating proteins (RIPs) with distinct expression patterns have similar requirements for proenzyme activation
Autor: | Hank W. Bass, Christopher Zinselmeier, Gregory R. OBrian, Rebecca S. Boston, Julie E. Krawetz, Jeffrey E. Habben |
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Rok vydání: | 2004 |
Předmět: |
Enzyme Precursors
DNA Plant Sequence Homology Amino Acid Physiology Ribosome-inactivating protein Molecular Sequence Data Restriction Mapping RNA Sequence alignment Plant Science Ribosomal RNA Biology Zea mays Conserved sequence Enzyme Activation Enzyme activator Biochemistry RNA Plant Amino Acid Sequence Sequence Alignment Peptide sequence Gene Conserved Sequence Plant Proteins |
Zdroj: | Journal of Experimental Botany. 55:2219-2233 |
ISSN: | 1460-2431 |
DOI: | 10.1093/jxb/erh243 |
Popis: | Ribosome-inactivating proteins (RIPs, EC 3.2.2.22) are potent naturally occurring toxins found in numerous and diverse plant species. The maize RIP is unusual among the plant RIPs because it is synthesized as an inactive precursor (also known as maize proRIP1 or b-32). The proenzyme undergoes proteolytic activation that results in the removal of the NH(2)-terminal, the COOH-terminal, and internal sequences to form a two-chain holoenzyme capable of irreversibly modifying the large rRNA. The characterization of a second maize RIP (RIP2), encoded by the gene designated Rip3:2 is described here. Low levels of Rip3:2 RNA were detected in roots, shoots, tassels, silks, and leaves, but the Rip3:2 gene, unlike the Rip3:1 gene, is not under the control of the transcriptional activator Opaque-2. Instead, its expression was up-regulated by drought. Rip3:2 encodes a 31.1 kDa polypeptide that is very similar to proRIP1 in regions corresponding to those found in the active protein and the NH(2)-terminal extension. A 19-amino-acid internal portion of proRIP2 has little similarity to the proRIP1 sequence except that both are very rich in acidic residues. RIP activity assays revealed that Rip3:2 encodes a polypeptide that acquires RNA-specific N-glycosidase activity after proteolytic cleavage. Accumulation as inactive proenzymes may therefore be a general feature of maize RIPs. Differential regulation of the two RIP genes suggests that the corresponding proteins may be involved in defence-related functions with one being regulated developmentally and the other being responsive to an environmental stimulus. |
Databáze: | OpenAIRE |
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