Verification, characterization and tissue-specific expression of UreG, a urease accessory protein gene, from the amphioxus Branchiostoma belcheri.

UreG genes have been found in bacteria, fungi and plants but have not yet identified in animals, although a putative UreG-like gene has been documented in sea urchin. In the course of a large-scale sequencing of amphioxus gut cDNA library, we have identified a cDNA with high similarity to UreG genes. Both reverse transcription-polymerase chain reaction and nested polymerase chain reaction, as well as in situ hybridization histochemistry, verified that the cDNA represented an amphioxus UreG gene (AmphiUreG) rather than a microbial contaminant of the cDNA library. This is further supported by the presence of urease activity in amphioxus gut, gill and ovary. AmphiUreG encodes a deduced protein of 200 amino acid residues including a highly conserved P-loop, bearing approximately 46%-49%, 44%-48%, and 29%-37% similarity to fungal, plant and bacterial UreG proteins, respectively. It shows a tissue-specific expression pattern in amphioxus, and is especially abundant in the digestive system. This is the first UreG gene identified in animal species.