On the characterization of the putative S20-Thx operon of Thermus thermophilus

A putative operon of the ribosomal proteins S20 and Thx has been determined in a 1.4 kb sequenced region of T. thermophilus genomic DNA. Both genes ha ve a promoter sequence 29 nt upstream of ORF1, possess their own Shine-Dalg arno motifs (GGAG) and are separated by only 9 nucleotides, a feature chara cteristic of the compact Thermus thermophilus genome. This is a novel arran gement, since Thx is unique to the Thermus bacteria and in all other prokar yotes the S20 gene is monocistronic. Our results, in conjunction with the r ecent finding that Thx is located on the top of the head of the 30S subunit in a cavity between multiple RNA elements stabilizing them with its positi ve charge, corroborate the observation that thermophilic ribosomes require constituents with special features for their stabilization at high temperat ures.