Sequence variations in the large-subunit ribosomal RNA gene of Ammonia (Foraminifera, Protozoa) and their evolutionary implications.
An unusually high divergence was observed in the ribosomal RNA genes of a free-living population of foraminifera belonging to the genus Ammonia. The sequences of a large-subunit (LSU) rDNA expansion segment D1 and flanking regions were obtained from 20 specimens named Ammonia sp. 1 and Ammonia sp. 2. The sequence divergence between the two species averages 14%. Within each species it ranges from 0.2% to 7.1% in Ammonia sp. 1 and from 0.7% to 2.3% in Ammonia sp. 2. We did not find two specimens having identical sequences. Moreover, in opposition to the generally accepted view, rDNA sequence variations were also found within a single individual. The variations among several rDNA copies in a single specimen of Ammonia may reach up to 4.9%. Most of the observed variations result from multiplication of CA or TA serial repeats occurring in two particularly variable regions. For single base changes, C-T transitions are most frequently observed. We discuss the evolution of expansion segments and their use for phylogenetic studies.
Holzmann
M
M
Institut für Paläontologie der Universität Wien, Austria.
Piller
W
W
Pawlowski
J
J
D000818:Animals; D001483:Base Sequence; D005075:Biological Evolution; D016054:DNA, Protozoan / Q000737:chemistry / Q000235:genetics*; D004275:DNA, Ribosomal / Q000737:chemistry / Q000235:genetics*; D056890:Eukaryota / Q000235:genetics*; D017125:Genes, Protozoan; D014644:Genetic Variation; D008969:Molecular Sequence Data; D010802:Phylogeny; D016053:RNA, Protozoan / Q000737:chemistry / Q000235:genetics; D012335:RNA, Ribosomal / Q000235:genetics; D012689:Sequence Homology, Nucleic Acid
D016054:DNA, Protozoan; D004275:DNA, Ribosomal; D016053:RNA, Protozoan; D012335:RNA, Ribosomal