The 5S ribosomal RNA sequences have been determined for the rhodoplast of the red alga Porphyra umbilicalis and the chloroplast of the conifer Juniperus media. The 5S RNA sequence of the Vicia faba chloroplast is corrected with respect to a previous report. A survey of the known sequences and secondary structures of 5S RNAs from plastids and cyanobacteria shows a close structural similarity between all 5S RNAs from land plant chloroplasts. The algal plastid 5S RNAs on the other hand show much more structural diversity and have certain structural features in common with bacterial 5S RNAs. A dendrogram constructed from the aligned sequences by a clustering algorithm points to a common ancestor for the present-living cyanobacteria and the land plant plastids. However, the algal plastids branch off at an early stage within the plastid-cyanobacteria cluster, before the divergence between cyanobacteria and land plant chloroplasts. This evolutionary picture points to the occurrence of multiple endosymbiotic events, with the ancestors of the present algal plastids already established as photosynthetic endosymbionts at a time when the ancestors of the present land plant chloroplasts were still free-living cells.

The 5s ribosomal ribonucleic acid (rRNA) sequences were determined for Bacteroides fragilis, Bacteroides thetaiotaomicron, Bacteroides capillosus, Bacteroides veroralis, Porphyromonas gingivalis, Anaerorhabdus furcosus, Fusobacterium nucleatum, Fusobacterium mortiferum, and Fusobacterium varium. A dendrogram constructed by a clustering algorithm from these sequences, which were aligned with all other hitherto known eubacterial5S rRNA sequences, showed differences as well as similarities with respect to results derived from 16s rRNA analyses. In the 5s rRNA dendrogram, Bacteroides clustered together with Cytophaga and Fusobacterium, as in 16s rRNA analyses. Intraphylum relationships deduced from 5s rRNAs suggested that Bacteroides is specifically related to Cytophaga rather than to Fusobacterium, as was suggested by 16s rRNA analyses. Previous taxonomic considerations concerning the genus Bacteroides, based on biochemical and physiological data, were confirmed by the 5s rRNA sequence analysis.The genus Bacteroides as described by Holdeman et al. (12) consists of more than 40 species which vary considerably in physiological, biochemical, and chemical properties and possess deoxyribonucleic acid (DNA) base compositions within the range from 28 to 61 mol% guanine plus cytosine (G+C). It is now generally accepted that a DNA base composition difference of more than 10 mol% G+C implies that the species concerned are unrelated at the generic level, yet notable exceptions occur (25). On the basis of physiological and biochemical properties, such as peptidoglycan composition, acid end products, lipids, and fatty acids (for a review see reference 30), various proposals have been made to exclude certain species from the genus Bacteroides (3, 30). Many of these proposals are in good agreement with ribosomal ribonucleic acid (rRNA) homology data (17). Thus, many of the species listed in Bergey's Manual of Systematic Bacteriology (12) have now been given separate generic status (1, 2, 4, 23,28,29,[31][32][33]. Recently, it has been suggested (3) that only members of the so-called "Bacteroides fragilis group" (viz

5s rRNA sequences were determined for the green sulphur bacteria Chlorobium limicola, Chlorobium phaeobacteroides and Prosthecochloris aestuarii, for Thermomicrobium roseum, which is a relative of the green non-sulphur bacteria, and for Cytophaga aquatilis, Cytophaga heparina, Cytophaga johnsonae, Flavobacterium breve, Flexibacter sp. and Saprospira grandis, organisms allotted to the phylum 'BacteroidepCytophagaFlavobacterium' and relatives as determined by 16s rRNA analyses. By using a clustering algorithm a dendrogram was constructed from these sequences and from all other known eubacterial5S RNA sequences. The dendrogram showed differences, as well as similarities, with respect to results obtained by 16s RNA analyses. The 5s RNA sequences of green sulphur bacteria were closely related to one another, and to a cluster containing 5s RNA sequences from Bacteroides and its relatives, including Cytophaga uquatilis. 5s RNA sequences of all other representatives of the 'Bacteroides-Cytophaga-Flavobacterium' phylum as distinguished by 1 6 s RNA analysis failed to group with Bacteroides and related clusters. On the basis of 5s RNA sequences, Thermomicrobium roseum clustered with Chlorofixus aurantiacus, as was expected from 16s RNA analysis.

The 5 S rRNA sequence was determined for the bacterium ~erpetosiphon strain Senghas Wie 2. It is the first 5 S RNA sequence reported for a member of the eubacterial phylum defined by green non-sulfur bacteria. The sequence fits into a consensus secondary structure model for eubacterial 5 S RNA. At four positions, the sequence shows substitutions with respect to strongly conserved nucleotides found in other hitherto examined eubacterial 5 S RNAs.

5s rRNA sequences were determined for the myxobacteria Cystobacter fuscus, Myxococcus coralloides, Sorangium cellulosum, and Nannocystis exedens and for the radioresistant bacteria Deinococcus radiodurans and Deinococcus radiophilus. A dendrogram was constructed by using weighted pairwise grouping based on these and all other previously known eubacterial5S rRNA sequences, and this dendrogram showed differences as well as similarities compared with results derived from 16s rRNA analyses. In the dendrogram, Deinococcus 5s rRNA sequences clustered with 5s rRNA sequences of the genus Thermus, as suggested by the results of 16s rRNA analyses. However, in contrast to the 16s rRNA results, the Deinococcus-Thermus cluster divided the 5s rRNA sequences of the alpha subdivision of the class Proteobacteria from the 5s rRNA sequences of the beta and gamma subgroups of the Proteobacteriu. The myxobacterial5S rRNA sequence data failed to confirm the existence of a delta subgroup of the class Proteobacteria, which was suggested by the results of 16s rRNA analyses.The genus Deinococcus consists of organisms which have spherical cells that grow in pairs or tetrads, possess distinct cell wall layers and an outer membrane, and stain gram positively (21). Their peptidoglycan type is A3P (31), with L-ornithine as a dibasic amino acid, and about one-quarter of the total fatty acid composition consists of palmitoleate (21); the phospholipids do not include phosphatidylglycerol, diphosphatidylglycerol, or derivatives of these compounds (3, but rather have a phosphoglycolipid as the major component (9). Menaquinones are fully unsaturated, with eight isoprene units (50). The genus is known for its outstanding ability to cope with the effects of gamma and UV irradiation, a property presumably related to polyploidy and cell division fine structure (21), as well as to the availability of effective repair mechanisms (20). Also, a rather complicated cell wall fine structure (17, 32, 33, 38, 49) of substantial chemical complexity (48, 49), together with a broad carotenoid selection and a rather peculiar polar lipid composition (5), is thought to play a part in minimizing the effects of free-radical formation (5, 21).A multitude of taxonomic (ll), chemotaxonomic (2, 14), and phylogenetic studies in which workers used both 16s rRNA catalog data (2, 14, 35) and full sequence information (42) have revealed and confirmed the isolated position of the genus Deinococcus with respect to the other gram-positive organisms. Phylogenetically and chemotaxonomically , the genus Deinococcus has been found to be specifically related to the gram-negative genera Deinobacter (24) and Thermus (14, 42), thus forming one of the 10 major phyla that are discernible on the basis of 16s rRNA analyses (45, 46). These three genera share a common peptidoglycan type (A3P) (31) and have unsaturated menaquinones with eight isoprene units as their principal isoprenoid quinones (9, 14, 24, 48, 50). On the basis of 5s rRNA analyses, the genus Thermus has been connected with two ...