165-235 AND 23S-5S INTERGENIC SPACER REGIONS OF STREPTOCOCCUS-THERMOPHILUS AND STREPTOCOCCUS-SALIVARIUS, PRIMARY AND SECONDARY STRUCTURE

The 16S-23S intergenic spacer region (spacer region 1) of Streptococcu s salivarius, S. thermophilus, and Lactococcus lactis subsp. cremoris and the 23S-5S intergenic spacer region (spacer region 2) of S. saliva rius and L. lactis subsp. cremoris were sequenced and compared with th e spacer regions 1 and 2 of other streptococci. A high degree of intra specific conservation was observed for S. thermophilus and L. lactis, and very similar sequences were found for S. salivarius and S. thermop hilus. Whereas spacer region 1 is highly conserved in the genus Strept ococcus sensu-stricto, only the tRNA gene and the rRNA processing stem s are highly conserved in the three genera: Streptococcus sensu-strict o, Lactococcus, and Enterococcus. The presence of a unique tRNA(Alu) g ene without the 3' terminal CCA sequence seems to be a general feature of the streptococci spacer region 1. A secondary structure model was built to show the interaction between the spacer regions 1 and 2 of S. thermophilus and S. salivarius. The rapid evolution of spacer region 1 in streptococci is in part due to insertions and deletions of small RNA stem/loop structures.