THE EFFECT OF RIBOSOME-INACTIVATING PROTEINS ON THE RIBOSOME FROM THEHYPERTHERMOPHILIC ARCHAEON SULFOLOBUS-SOLFATARICUS

Protein synthesis in the thermoacidophilic archaeon Sulfolobus solfata ricus (Ss) was inhibited by polynucleotide: adenosine glycosylase acti vity of some type 1 ribosome-inactivating proteins (RIP). The target o f RIP was S. solfataricus rRNA that was depurinated thus producing ina ctive ribosomes. The amount of RIP required to half-inactivated Ss-rib osomes was comparable to that needed for eubacterial ribosomes, but tw o orders of magnitude higher than that required for mammalian ribosome s. In addition, RIP treated Ss-ribosomes were also less efficient in s timulating the ribosome dependent GTPase activity of the S. solfataric us elongation factor 2 (SsEF-2) thus suggesting that the inhibition of protein synthesis was probably due to the lack of the interaction bet ween depurinated Ss-ribosomes and SsEF-2. Since SsEF-2 protects Ss-rib osomes against RIP activity it can be hypothesised that also on Ss-rib osomes the sites of interaction for the translocation factor 2 and the RIP are topographically close.