Investigation of a ribosomal RNA operon of Frankia sp. strain AcN14a.

Abstract

With the aim of increasing our plant knowledge of Frankia, we have investigated the structure of the ribosomal RNA genes from Frankia sp. strain AcN14a. A genomic library was constructed in EMBL3 and two types of clones, each containing a different set of rRNA genes, were identified by restriction analysis. The rRNA genes of Frankia AcN14a have been compared to those of E. Coli and other eubacterial species. Frankia AcN14a rRNA genes show over 98% idenity to those of Frankia ORS020606 and usually show over 80% identity to other actinomycete rRNA sequences. The mature 16S, 23S and 5S rRNAs are predicted to contain 1509, 3105 and 120 nucleotides, repectively. Thus, Frankia 16S rRNA is smaller than that of E. coli whereas the 23S rRNA of Frankia is longer than it E. coli counterpart. In spite of these size differences, all three rRNAs could be folded into secondary structures similar to the E. coli models and most tertiary interactions proposed for E. coli rRNAs could be formed in Frankia AcN14a 16S and 23S rRNAs. Finally, the potential usefulness of rRNA RFLP analysis for the categorization of Frankia isolates has been investigated. Hybridization of both 16S and 23S rDNA specific probes to total DNA digested with BamH1, revealed sufficient polymorphism to allow classification of twenty-six isolates into six groups (A to F). In addition, eight other isolates exhibit unique patterns. (Abstract shortened by UMI.)