A. Gluck et al., THE RIBOSOMAL-RNA IDENTITY ELEMENTS FOR RICIN AND FOR ALPHA-SARCIN - MUTATIONS IN THE PUTATIVE CG PAIR THAT CLOSES A GAGA TETRALOOP, Nucleic acids research, 22(3), 1994, pp. 321-324
alpha-Sarcin is a ribonuclease that cleaves the phosphodiester band on
the 3' side of G4325 in 285 rRNA; ricin A-chain is a RNA N-glycosidas
e that depurinates the 5' adjacent A4324. These single covalent modifi
cations inactivate the ribosome. An oligoribonucleotide that reproduce
s the structure of the sarcin/ricin domain in 28S rRNA was synthesized
and mutations were constructed in the 5' C and the 3' G that surround
a GAGA tetrad that has the sites of toxin action. Covalent modificati
on of the RNA by ricin, but not by alpha-sarcin, requires a Watson - C
rick pair to shut off a putative GAGA tetraloop. Either the recognitio
n elements for the two toxins are different despite their catalyzing c
ovalent modification of adjacent nucleotides in 285 rRNA or there are
transitions in the conformation of the alpha-sarcin/ricin domain in 28
S rRNA and one conformer is recognized by alpha-sarcin and the other b
y ricin A-chain.