Molecular Cloning And Evolution Of The AmphiS23 Gene And AmphiL35 Gene From Amphioxus Branchiostoma Belcheri Tsingtauense

In this paper, the complete cDNA and deduced amino acid sequences of the ribosomal proteins S23 (AmphiS23) and L35 (AmphiL35) have been identified from amphioxus Branchiostoma belcheri tsingtauense gut cDNA library. AmphiS23 cDNA is 546 bp long, and consisted of a 26 bp 5' untranslated region (UTR), an open reading frame (ORF) of 432 bp and an 88 bp 3' UTR. The ORF encoded a 143 amino acid protein with a calculated molecular mass of 15,851 Da and an isoelectric point (pI) of 10.706. AmphiL35 cDNA comprises 473 bp, and included a 5' UTR of 27 bp, an ORF of 372 bp and a 3' UTR of 74 bp. The ORF encoded a 123 amino acid protein with a calculated molecular mass of 14,543 Da and a pI of 10.809. AmphiL35 has an excess of basic residues versus acidic ones(4:l), which is close to the proportion of basic residues versus acidic ones in the amino acid sequence of other L35 proteins.Compared with those of the other known S23 and L35 proteins from various eukaryotic organisms in the Genbank database, AmphiS23 shares more than 83% identity to its homologues in the vertebrates and more than 84% identity to those in the invertebrates, which shows AmphiS23 is quite conservative in evolution; while AmphiL35 is more than 63% identical to its counterparts in the vertebrates, and more than 52% identical to those in the invertebrates. Meanwhile, according to the comparison of twelve kinds of L35 proteins from different eukaryotic species in this paper, the amino acid sequence similarity between AmphiL35 and L35 proteins from invertebrates is 62.6-65.9% and the similarity between AmphiL35 and L35 proteins from vertebrates is 75.6-81.3%. These data seem to demonstrate that amphioxus is closer to the vertebrates.In the Southern blot analysis, hybridization of the DIG labeling probe to digests of genome DNA demonstrates the existence of 1-2 copies of S23 gene and 2-3 copiesof L35 gene in the genome of amphioxus B. belcheri tsingtauense. This is in sharp contrast to the presence of 6-13 copies of S23 gene and 15-17 copies of L35 gene in rat genome. It is clear that the housekeeping genes like S23 and L35 had undergone a large-scale duplication in the vertebrate lineage, just like luxury genes.