The -agarase C gene (agaC) of a marine bacterium, Vibrio sp. strain PO-303, consisted of 1,437 bp encoding 478 amino acid residues. -Agarase C was identified as the first -agarase that cannot hydrolyze neoagarooctaose and smaller neoagarooligosaccharides and was assigned to a novel glycoside hydrolase family.Agar is a hydrophilic polysaccharide contained in the cell walls of agarophyte red algae and is composed of agarose and agaropectins (7). -Agarases (EC 3.2.1.81), which hydrolyze agar, are useful tools for the preparation of neoagarooligosaccharides and the isolation of protoplasts from the algae (4). We isolated a -agarase-producing bacterium, Vibrio sp. strain PO-303, from a sea environment. Among the -agarases secreted by the organism, -agarase C was found to be capable of forming neoagarooligosaccharides longer than neoagarohexaose (DP6) from agar (3). In this paper, we describe the cloning and expression of the -agarase C gene (agaC) and the characterization of the recombinant enzyme (rAgaC).Cloning of the agaC gene. A 759-bp DNA fragment was amplified by PCR using chromosomal DNA of strain PO-303 as a template and the degenerate primers GCNAAYTAYAC NGCNWSNAAYGC and CCRTTNGCRAANACNACNGG, composed according to the N-terminal amino acid sequences of -agarase C and its protease-digested fragment. Sequence analysis showed that the 759-bp fragment derived from the agaC gene. The XbaI-digested chromosomal DNA fragments were purified and self-ligated with a Takara ligation kit, version 2. The upstream and downstream regions of the 759-bp fragments were amplified by inverse PCR with the self-ligated DNA fragments as templates and two outward-facing primers designed according to the sequence given above. The PCR product was cloned into a pT7Blue-2 vector (Novagen) and sequenced. The sequencing results showed that the agaC gene consisted of 1,437 bp encoding 478 amino acid residues with a predicted molecular weight of 50,922. A potential ribosome-binding site (AGGAGA) and the Ϫ35 and Ϫ10 promoter regions were identified upstream of the coding region (15, 17). A possible transcription terminator was found downstream of the TAG termination codon. Comparison of the deduced amino acid sequence with the entries in databases suggested that -agarase C might belong to a novel glycoside hydrolase (GH) family, because no known GH was found to have homology with it.Expression and purification of rAgaC. The agaC gene without the signal sequence was amplified by PCR from strain PO-303 chromosomal DNA by using primers GGTGTACAT ATGGCTAACTATACTGCCAGTAA and GCGGCCCTCG AGCTATTGGCAAGTATAACCTG, which contained artificial NdeI and XhoI sites (italicized). The amplified DNA fragment was digested with NdeI and XhoI and was ligated into a pET22b(ϩ) vector (Novagen) to construct pETAgaC. Escherichia coli BL21(DE3) strains (Novagen) harboring pETAgaC were cultivated for 12 h at 25°C in 1,000 ml of Luria-Bertani medium containing ampicillin and were induced with 1 mM isopropyl--D-thiogalactopyranoside. The cells harvested by ce...