TY - JOUR

T1 - Comparison of primary and secondary 26S rRNA structures in two Tetrahymena species: evidence for a strong evolutionary and structural constraint in expansion segments

AU - Engberg, J

AU - Nielsen, Henrik

AU - Lenaers, G

AU - Murayama, O

AU - Fujitani, H

AU - Higashinakagawa, T

N1 - Keywords: Animals; Base Sequence; Evolution; Molecular Sequence Data; Nucleic Acid Conformation; RNA, Ribosomal; Tetrahymena; Tetrahymena pyriformis

PY - 1990

Y1 - 1990

N2 - We have determined the nucleotide sequence of the 26S large subunit (LSU) rRNA genes for two Tetrahymena species, T. thermophila and T. pyriformis. The inferred rRNA sequences are presented in their most probable secondary structures based on compensatory mutations, energy, and conservation criteria. The majority of the nucleotide changes between the two Tetrahymena LSU rRNAs and the positions of a relatively large deletion and of the processing cleavage sites resulting in the generation of the hidden break are all located within the so-called divergent domains or expansion segments. These are regions within the common core of secondary structure where expansions have taken place during the evolution of the rRNA of higher eukaryotes. The dispensable nature of some of the expansion segments has been taken as evidence of their non-functionality. However, our data show that a considerable selective constraint has operated to preserve the secondary structure of these segments. Especially in the case of the D2 and D8 segments, the presence of a considerable number of compensatory base changes suggests that the secondary structure of these regions is of functional importance. Alternatively, these expansion segments may have maintained characteristic folding patterns because only such structures are being tolerated within otherwise functionally important regions.

AB - We have determined the nucleotide sequence of the 26S large subunit (LSU) rRNA genes for two Tetrahymena species, T. thermophila and T. pyriformis. The inferred rRNA sequences are presented in their most probable secondary structures based on compensatory mutations, energy, and conservation criteria. The majority of the nucleotide changes between the two Tetrahymena LSU rRNAs and the positions of a relatively large deletion and of the processing cleavage sites resulting in the generation of the hidden break are all located within the so-called divergent domains or expansion segments. These are regions within the common core of secondary structure where expansions have taken place during the evolution of the rRNA of higher eukaryotes. The dispensable nature of some of the expansion segments has been taken as evidence of their non-functionality. However, our data show that a considerable selective constraint has operated to preserve the secondary structure of these segments. Especially in the case of the D2 and D8 segments, the presence of a considerable number of compensatory base changes suggests that the secondary structure of these regions is of functional importance. Alternatively, these expansion segments may have maintained characteristic folding patterns because only such structures are being tolerated within otherwise functionally important regions.

M3 - Journal article

C2 - 2115930

VL - 30

SP - 514

EP - 521

JO - Journal of Molecular Evolution

JF - Journal of Molecular Evolution

SN - 0022-2844

IS - 6

ER -