The cDNA AmphiARF , encoding a novel member of ARF family was for the first time identified from the gut cDNA library of amphioxus Branchiostoma becheri tsingtauense . The deduced amino acid sequence includes the motifs involved in GTP binding (DVGG, NKQD and SAK) and hydrolysis (GXDXXGK), and a glycine at position 2 for N-terminal myristoylation, which are all characteristic of ARFs. However, it has a 46 amino acid C-terminal extension (positions 183-227), which was not found in any ARF family previously described including ARF-like proteins. This suggests that AmphiARF is a new member of ARF family, which was also supported by the phylogenetic analysis. It is highly likely that the extended C-terminal of AmphiARF is a novel addition occurring after cephalochordate/vertebrate split. Northern blotting analysis revealed that AmphiARF transcript was present in all tissues examined, consistent with the involvement of ARFs in the fundamental role like vesicular trafficking of proteins.