A functional plasmid-borne rrn operon in soil isolates belonging to the genus Paracoccus

Abstract

Plasmid analysis of isolates from a smallParacoccuspopulation revealed that all 15 representatives carried at least one endogenous plasmid of 23 or 15 kb in size, in addition to further plasmids of different sizes. It was shown by restriction analysis and hybridization that the 23 and 15 kb plasmids from the different isolates were identical or very similar to each other. By partial sequencing of pOL18/23, one of the 23 kb plasmids, a completerrnoperon with the structural genes for 16S, 23S and 5S rRNA, two genes for tRNAIleand tRNAAlawithin the spacer between the 16S and 23S rRNA genes, and a final tRNAfMetat the end of the operon were discovered. Expression of a green fluorescent protein gene (gfp) after insertion of a DNA fragment from the region upstream of the rRNA genes into a promoter-probe vector demonstrated that therrnpromoter region is functional. Therrnoperon encoded by plasmid pOL18/23 is the first completerrnoperon sequenced from a strain of the genusParacoccus, and only the second example of anrrnoperon on a small plasmid.