Verification, Expression And Evolution Of NifU-like Gene From The Amphioxus Branchiostoma Belcheri Tsingtauense

Amphioxus or lancelet, a protochordate, has long been regarded as a model animal for gaining understanding of the origin of vertebrates. Its genetic information on gene sequence and expression pattern has been widely used for interspecies comparative genome studies and developmental homology analysis. In this paper, the cloning, verification, expression and phylogenetic analysis of nifU-like gene from the gut cDNA library of amphioxus Branchiostoma becheri tisingtauense are carried out.In the course of expressed sequence tag (EST) generation from gut cDNA library of adult amphioxus Branchiostoma belcheri, we isolate a clone L052 exhibiting identity to nifU-like gene. The aims of this study are thus to verify that the gene is from amphioxus B. belcheri, and if so, to examine its expression profile.The clone L052 (GenBank accession number: AY279520) obtained from the gut cDNA library of amphioxus B. belcheri is 630 bp long, and its longest open reading frame consisting of 495 bp codes for a protein of 164 amino acid residues with a predicted molecular weight of about 17.51 kDa and an isoelectric point of 7.3. There are a start codon ATG at the 5 end of the deduced protein, and a stop codon TAA at its 3'end. The 5'-untranslated region (UTR) is 55 bp long with an in-frame stop codon (TGA), and the 3'-UTR is 30 bp long with a polyadenylation tail (Figure 1). Therefore, the clone L052 encodes a full-length sequence protein.Initial BLASTP search at NCBI reveales that the protein encoded by clone L052 shares 73% identities (90/122) to the N-terminal region of NifU from the bacterium A. vinelandii (Genbank accession number: EAM05767). It is thus further compared with other members of NifU-like family. The protein encoded by L052 has a U-type motif (C-X26-C-X43-C), a unique feature of NifU-like proteins, and shares 66-86% identity to all known NifU-like proteins. Therefore, the clone L052 codes for a NifU-like protein.