Nucleotide sequences of the six very small molecules of Trypanosoma cruzi ribosomal RNA (original) (raw)

1991, Nucleic Acids Research

EMBL accession nos X54474-X54479 (incl.) Ribosomal RNA (rRNA) molecules are considered very good phylogenetic markers because they are shared by all prokaryotic and eukaryotic cells, as a constitutive part of the very ancient protein synthesis machinery, the ribosomes. It seems their primary and secondary structure as well as the relative position of the genes or gene fragments (exons) within the ribosomal cistron, reflect the phylogenetic distances between living groups of organisms. There are some remarkable differences between trypanosomatid rRNA molecules and those of most eukaryotic organisms. First, trypanosomatids have four very small rRNAs in addition to the typical eukaryotic 5S and 5.8S-like species and all six mature molecules are associated with the 28S-like species of the large ribosomal subunit. Second, the genes for three of the extra rRNAs: M2, M4 and M6, are coded near the 3' end of the genes for the 28S-like species and the gene for Ml is located between the two exons for the constituents (alpha and beta) of the 28S-like molecule (1, 2). The remaining species, M3 and M5 are considered 5.8S and 5S-like, respectively. These small rRNA molecules were directly sequenced employing the method of Donis-Keller (3) using the enzymes TI, U2, Phy M and B. cereus. The length, in number of bases, the relative composition of purine and pyrimidine bases, and the accession numbers in EMBL are presented in . The percent homology with the corresponding molecules of Crithidia fasciculata (4) and Trypanosoma brucei (5, 6) calculated with CLUSTAL package , shows the very close relationship between these molecules, but that M6 is relatively more variable .