title: Cyanobacterial evolution: results of 16S ribosomal ribonucleic acid sequence analyses.
abstract: We report here the sequences of oligonucleotides released by T1-ribonuclease digestion of the 16S ribosomal RNA's (rRNA's) of unicellular cyanobacteria Agmenellum quadruplicatum (strain BG-1) and Synechococcus 7502. We compare them with sequences previously obtained for the 16S RNA's of six other cyanobacteria and two chloroplasts, and conclude that: (i) Synechocystis-like unicells form a discrete cluster which also (and surprisingly) includes Agmenelium quadruplicatum, usually considered to be a Synechococcus; (ii) filamentous cyanobacteria of the genera Nostoc and Fischerella arose from within the Synechocystis group; (iii) phylogenetic diversity (and hence presumably evolutionary antiquity) within the Synechococcus group is very great; and (iv) red algal chloroplasts are of definite cyanobacterial origin, while Euglena chloroplasts are of separate and quite possibly noncyanobacterial origin. We also present the results of a computer-aided search among the 10 oligonucleotide 'catalogues' for families of related but nonidentical sequences. Examination of these families reinforces the above conclusions.
mesh_terms: D001483:Base Sequence; D005075:Biological Evolution; D000458:Cyanobacteria / Q000032:analysis* / Q000235:genetics; D009843:Oligoribonucleotides / Q000032:analysis; D012335:RNA, Ribosomal / Q000032:analysis*
chemical_list: D009843:Oligoribonucleotides; D012335:RNA, Ribosomal