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We have isolated a genomic clone containing rice 5 S ribosomal RNA (rRNA)-encoding genes (rDNA). The clone contains 10 repeat units of 290 bp, plus 2.0 kb of flanking genomic sequence at one border. Sequencing of individual repeat units shows that the sequence of the 5 S rRNA coding region is very similar to that reported for other flowering plants, while the nontranscribed spacer region is diverged. Genomic DNA-blot analysis indicates that 5 S rDNA occurs in long tandem arrays. A rice 5 S rRNA-binding protein gene (RL5) was previously idolated and sequenced [Kim, J.-K., and Wu, R. (1993) Plant Mol. Biol. 23, 409-413]. Amino acid sequence analysis of the RL5 protein revealed that it has many intriguing features. These include the presence of three repeated amino acid sequences and the conservation of glycine residues, which may be important for 5 S rRNA/RL5 protein interactions. Genomic DNA-blot analysis indicates that there are fewer copies of the RL5 gene in rice than in other eukaryotes. The RL5 gene appears to be constitutively expressed at high levels in rice tissues.
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