In vitro processing of the 16S rRNA of the thermophilic archaeon Sulfolobus solfataricus

In this paper we have analyzed the processing in vitro of the 16S rRNA of t he thermophilic archaeon Sulfolobus solfataricus, using pre-rRNA substrates transcribed in vitro and different protein preparations as the source of p rocessing enzymes. We show that the 5' external transcribed spacer of the S , solfataricus pre-rRNA transcript contains a target site for a specific en donuclease, which recognizes a conserved sequence also existing in the earl y AO and 0 processing sites of Saccharomyces cerevisiae and vertebrates. Th is site is present in other members of the kingdom Crenarchaeota but appare ntly not in the Euryarchaeota, Furthermore, S, solfataricus pre-16S RNA is processed within the double-helical stem formed by the inverted repeats fla nking the 16S RNA sequence, in correspondence with a bulge-helix-bulge moti f, The endonuclease responsible for this cleavage is present in both the Cr enarchaeota and the Euryarchaeota, The processing pattern remained the same when the substrate was a 30S ribonucleoprotein particle instead of the nak ed RNA. Maturation of either the 5' or the 3' end of the 16S RNA molecule w as not observed, suggesting either that maturation requires conditions not easily reproducible in vitro or that the responsible endonucleases are scar cely represented in cell extracts.