The 16S-23S and 23S-5S rRNA spacer DNA regions (spacer regions 1 and 2, respectively) from and were amplified by PCR. Their nucleotide sequences were established and a secondary structure model showing the interaction between the two spacer regions was built. Whereas lactococci and are characterized by a single type of spacer region 1, the enterococci show a high degree of variability in this region; thus the spacer regions 1 with and without tRNAwere characterized. However, as shown for lactococci and , the tRNAgene does not encode the 3'-terminal CCA trinucleotide. A putative antitermination signal is found downstream from the tRNAgene. Based on comparison with and , a double-stranded processing stem is proposed. In , one of the three different types of spacer region 1 contains no tRNA, but displays a 107 nt insertion that forms a long stem-loop structure. A similar insertion (115 nt in length) was found in and base compensatory mutations preserve the ability to form the long stem-loop structure. Such insertions may correspond to mobile intervening sequences, as found in the 23S rRNA coding sequences of some Gram-negative bacteria. The spacer regions 1 and 2 from the three subgroups of streptococci were compared, and except for the tRNAgene and the double-stranded processing sites, little similarity was found, which opens large possibilities for future development of DNA-based typing methods.


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