Identification and Analysis of the Gap Region in the 23 S Ribosomal RNA from Actinobacillus

98021 Actinobacillus actinomycetemcomitans is a Gram-negative coccobacillus which can cause certain severe extra-oral infections as well as forms of human periodontal disease such as localized juvenile periodontitis. In contrast to many prokaryotic and eukary-otic species which exhibit an intact 23S ribosomal RNA (rRNA) molecule, examination of six A. actinomycetemcomitans strains-including three serogroup representative strains and two strains from non-human primates-revealed that this microorganism does not produce an intact 23S ribosomal RNA (rRNA) molecule but, rather, two smaller forms of 1.8 kb and 1.2 kb designated as 23Sa and 235 fragments. On the other hand, 14 other strains of Actinobacillus, Haemophilus, andPasteurella species demonstrated intact 23S rRNA. The sequence ofthe region ofthe 23S rRNA gene in A. actinomycetemcomitans strain ATCC 43718 containing the cleavage site was determined by dideoxynucleotide sequencing, while the location of the 3' and 5' termini of the 23Sa and 2351 fragments was resolved by S1 nuclease mapping and cDNA primer-extension. A deletion of 112 bases was noted in comparisons ofbase sequences from A. actinomycetemcomitans rRNA and rDNA. The DNA intervening sequence was localized to nucleotide 1180 of the Escherichia coli 23S rRNA map. While the primary structure ofthe gap region showed little homology with the gap regions described in other organisms, the secondary structure was similar to that previously described in the parasitic helminth Schistosoma japonicum. Restriction enzyme and nucleotide sequence analysis of the gap region in eight otherA. actinomycetemcomitans strains showed it to be highly conserved.