A new class of enzyme acting on damaged ribosomes: ribosomal RNA apurinic site specific lyase found in wheat germ.
A new enzyme, which we named ribosomal RNA apurinic site specific lyase (RALyase), is described. The protein was found in wheat embryos and has a molecular weight of 50 625 Da. The enzyme specifically cleaves the phosphodiester bond at the 3' side of the apurinic site introduced by ribosome-inactivating proteins into the sarcin/ricin domain of 28S rRNA. The 3' and 5' ends of wheat 28S rRNA at the cleavage site are 5'-GUACG-alpha-hydroxy-alpha, beta-unsaturated aldehyde and pGAGGA-3', demonstrating that the enzyme catalyzes a beta-elimination reaction. The substrate specificity of the enzyme is extremely high: it acts only at the apurinic site in the sarcin/ricin domain of intact ribosomes, not on deproteinized rRNA or DNA containing apurinic sites. The amino acid sequences of five endopeptidase LysC-liberated peptides from the purified enzyme were determined and used to obtain a cDNA sequence. The open reading frame encodes a protein of 456 amino acids, and a homology search revealed a related rice protein. Similar enzyme activities were also found in other plants that express ribosome-inactivating proteins. We believe that RALyase is part of a complex self-defense mechanism.
Ogasawara
T
T
Department of Applied Chemistry, Faculty of Engineering, Ehime University, Matsuyama, 790-8577 Japan.
Sawasaki
T
T
Morishita
R
R
Ozawa
A
A
Madin
K
K
Endo
Y
Y
D000595:Amino Acid Sequence; D001483:Base Sequence; D002852:Chromatography, Ion Exchange; D018076:DNA, Complementary; D004722:Endoribonucleases / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D037121:Plant Lectins; D018749:RNA, Plant / Q000737:chemistry / Q000378:metabolism; D012339:RNA, Ribosomal, 28S / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D012276:Ricin / Q000378:metabolism; D012639:Seeds / Q000201:enzymology; D013379:Substrate Specificity; D014908:Triticum / Q000201:enzymology* / Q000235:genetics
D018076:DNA, Complementary; D037121:Plant Lectins; D018749:RNA, Plant; D012339:RNA, Ribosomal, 28S; D011994:Recombinant Proteins; D012276:Ricin; D004722:Endoribonucleases; C402789:ribosomal RNA apurinic site specific lyase