Molecular Cloning And Evolution Of The AmphiL34 And AmphiS29 Gene From Amphioxus Branchiostoma Belcheri Tsingtauense

The complete cDNA and deduced amino acid sequences of ribosomal proteins L34 (AmphiL34) and S29 (AmphiS29) have been identified from amphioxus Branchiostoma belcheri tsingtauense in this paper. AmphiL34 cDNA consists of 435 bp, including a 33 bp 5' untranslated region (UTR), an open reading frame (ORF) of 357 bp and a 45 bp 3' UTR. The ORF encodes a 118 amino acid protein with a calculated molecular mass of about 13.6 kDa, and an isoelectric point of 11.44. AmphiL34 is a rather hydrophobic protein with 46 hydrophobic amino acids out of 118 residues, and has 34 basic amino acids mostly located in the N-terminal half of the deduced protein sequence, and 4 acidic amino acids mostly situated in the C-terminal half. Moreover, AmphiL34 has the tetrapeptide RXXR. All of the characters are identical to other L34 proteins.AmphiS29 cDNA comprises 453 bp, and contains a 5' UTR of 21 bp, an ORF of 171 bp and a 3' UTR of 261 bp. The ORF encodes a 56 amino acid protein with a calculated molecular mass of about 6.6 kDa and an isoelectric point of 9.79. AmphiS29 has a zinc finger-like domain, and has an excess of basic residues over acidic ones (10:2), which is close to the proportion of basic residues versus acidic ones in the amino acid sequence of other S29 proteins.The deduced protein sequence of AmphiL34 is compared with that of other 11 known L34 from diverse organisms. It shows that at the amino acid level, AmphiL34 shares 53.6-67.5% identity to its known counterparts. Comparison of the deduced AmphiS29 amino acid sequence with that of its 10 counterparts shows 66.1-78.6% amino acid sequence identity to S29 family members of other eukaryotes including the invertebrates. The phylogenetic tree deduced from the conserved sequences ofAmphiL34 and AmphiS29 and other known counterparts indicates the positions of AmphiL34/AmphiS29 are intermediate between the vertebrate L34/S29 and the invertebrate L34/S29. These are in line with the notion that amphioxus is an organism transitional from invertebrate to vertebrate in phylogeny. The visible homology of AmphiL34 and AmphiS29 to their known counterparts indicates that L34 and S29 are highly conserved during evolution.In the Southern blot analysis, hybridization of the DIG labeling probe to digests of genome DNA suggests that there is one copy of the AmphiL34, and there are 2-3 copies of the AmphiS29. It is clear from the comparison of the number of AmphiL34 and AmphiS29 genes with that of rat L34 and S29 genes that duplication of L34 and S29 genes occurred in vertebrates like rat. It therefore appears that the housekeeping ribosomal proteins genes such as L34 and S29 also underwent large-scale duplication during the early chordate evolution.