As a precursor of the major yolk protein vitellin (Vn), vitellogenin (Vg) has been studied in crustacean for decades, mainly in shrimp. However, little is known about the Vg molecule in crabs. In the present study, we report a cDNA encoding Vg in the marine crab Portunus trituberculatus, an important commercial species in aquaculture. The cDNA sequence is 7846 bp in length, containing a 7680 bp open reading frame, that encodes 2560 amino acid residues. The deduced amino acid sequence showed 32-75% identity with other known crustacean Vgs. Seven potential cleavage sites (RXXR) were identified in the deduced Vg precursor. SDS-PAGE and Westem blotting analysis demonstrated that Vns in the ovary of the mature crab consisted of three major polypeptides (102, 100 and 85 kDa). Northern blotting analysis revealed that Vg was mainly expressed in hepatopancreas in vitellogensis females. A Vg transcript was also identified in the ovary of the crab by reverse transcription-polymerase chain reaction analysis. (c) 2005 Elsevier Inc. All fights reserved.