RRNA gene clusters

Field, K. G., D. Gordon, T. Wright, M. Rappe, E. Urbach, K. Vergin, and S. J. Giovannoni. 1997. Diversity and depth-specific distribution of SAR11 cluster rRNA genes from marine planktonic bacteria. Applied and Environmental Microbiology 63 63-70. 

Although the number of rRNA operons varies within the cell the sequence of the rRNA in these multicopy genes is usually identical or nearly so [38]. One exception is the rRNA genes in H. marismortui. The two 168 rRNA genes differ significantly [39] and these differences are mainly clustered within the central domain of the 168 rRNA. Of even greater interest is the observation that both genes are expressed and the 168 rRNA molecules assembled into active 708 ribosomes. 

Phylogenetic analysis revealed that the 16S rRNA genes of solventogenic clostridia group into two distinct clusters (Figure 9.3). One cluster is formed by all C. acetobutylicum strains sequenced so far. All strains have identical 16S rRNA sequences except for one substitution in strain GXAS18-1. 

---