Precise characterization of rDNA genes by intraspecies and inter-loci comparison of rDNA sequences and biochemical analysis of ribosomal RNA molecules in Agrobacterium tumefaciens.

Annotation of rRNA genes has been incomplete in Agrobacterium species although a number of Agrobacterial rDNA fragments have been sequenced. In this study, precise characterization of rRNA operons (rrn) was carried out in two biovar 1 strains, C58 and MAFF301001. Complete DNA sequencing of four rrns in MAFF301001 indicated that each operon codes for 16S, 23S and 5S rRNA as well as three tRNAs, trnIle, trnAla and trnMet. The genes and 16S-23S ITS of a given locus were exactly identical with those in the other three loci, except for a T-base loss in the 23S rRNA gene of rrnA and in the 5S rRNA gene of rrnB. Comparison with the four C58 rDNAs available in the DNA database indicated extensive sequence and size variations in the 23S rRNA gene, suggesting the presence of an intervening sequence (IVS). Biochemical RNA analysis, including Northern hybridization and 5’ end mapping, in MAFF301001 revealed 2886-base and 2571-base precursors, two 1.3-kb major fragments, a 150-base fragment and removal of an IVS for 23S rRNA. We confirmed similar biochemical characteristics in the C58 strain. The features of rDNA detected here enable correction of previously reported information about Agrobacterial rRNAs and rRNA genes and should be useful for phylogenetic considerations.