Sequence analysis of domains III and IV of the 23S rRNA gene of verticillate streptomycetes

Domains III and IV of the 23S rRNA gene of 25 strains of verticillate strep tomycetes were sequenced. None of the sequences was identical to any other, with regions of variability being restricted to parts of helices 54 and 64 . No relationships were detected between the similarities in the sequence a nd the assignment to phenetic clusters as defined by the numerical taxonomy studies. Limited agreement was also found between similarity of the sequen ces and DNA-DNA homology values. However, species (> 70 % DNA-DNA homology values)-specific diagnostic oligonucleotides generally could be defined, ex cept for Streptomyces baldaccii. Therefore the determination of the 23S rRN A sequence may be of greater value for fingerprinting individual strains th an for taxonomic or identification purposes.