EFFECTS AND MOLECULAR ACTION OF RIBOSOME-INACTIVATING PROTEINS ON RIBOSOMES FROM STREPTOMYCES-LIVIDANS

The effects of 29 type 1 and 2 type 2 ribosome-inactivating proteins ( RIPs) from plants on polyuridylic acid-directed polyphenylalanine synt hesis carried out by purified ribosomes from Streptomyces lividans wer e studied. only dianthin 32, saporins R1 and R3, momordin I, trichokir in, Hura crepitans RIP 5 from latex, cretins 2 and 3, and PAPs C, R, a nd S, inhibited polyphenylalanine synthesis. Both the type 2 RIPs rici n and volkensin were ineffective on translation. The magnesium concent ration affected the inhibition of translation to a considerable extent . Upon treatment with inhibitory RIPs, extraction of rRNA and further treatment with acid aniline, S. lividans ribosomes released an RNA fra gment of about 130 nucleotides. The 5' terminal sequence of this rRNA fragment was 5'-GAGGACCGGGACGGACGAACCUCUGGUGUGCCAGUUGU-3', similar to the sequence obtained in Escherichia coli. This indicates that the mos t probable molecular action of these RIPs on S. lividans and E. coli r ibosomes is the same: depurination of the rRNA at a site relevant to t he translation mechanism and that has been highly conserved throughout evolution.