Structure of the 5‐S Ribosomal RNA Gene and Its Adjacent Regions in Torulopsis utilis

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Abstract
A DNA segment spanning one repeating unit of ribosomal RNA(rRNA) genes in a yeast strain, Torulopsis utilis, has been cloned on a bacterial plasmid pBR322. The size of the cloned segment was about Mr, = 8.0 × 106. All of the genes for the four species of rRNA were linked on it, and there was a long spacer between the 5‐S and 18‐5 rRNA coding regions. The nucleotide sequences of the regions flanking the 5‐S rRNA gene were determined and compared with those in the corresponding regions of Saccharomyces cerevisiae [Valenzuela, P., Bell, G. I., Masiarz, F. R., DeGennaro, L. J., and Rutter, W. J. (1977) Nature, 267, 641–643; Maxam, A. M., Tizard, R., Skryabin, K. G., and Gilbert, W. (1977) Nature, 267, 643–645]. The sequence of the T. utilis 5‐S rRNA is identical with that of S. cerevisiae except for two residues at positions 18 and 61. However, its upstream region contained a quite different sequence, and a sequence which showed some homology was only found at positions – 21 to – 28. The sequences were d(T‐G‐T‐A‐A‐C‐C‐T) in T. utilis and d(T‐A‐T‐C‐A‐C‐C‐T) in S. cerevisiae. Although the presence of various repeat sequences having the same or opposite directions was noted, these repeats occurred at different positions in the two yeast species. In the downstream region, the common sequence was only seven dT deoxynucleotides, which occurred immediately after the 5‐S rRNA coding sequence. Significant direct and inverted repeat sequences were found in T. utilis, but such repeats are not seen in S. cerevisiae.