The extracellular poly(3-hydroxybutyrate) depolymerase gene from Akaligenes faecalis Tl was cloned into Escherichia coli DH1 by using the plasmid pUC8. An A. faecalis Ti genomic library was prepared in E. coli from a partial Sau3AI digest and screened with antibody against the depolymerase. Of the 29 antibody-positive clones, 1 (pDP14), containing about 4 kilobase pairs of A. (22), modified by the addition of achromopeptidase (TBL-1; 1.5 mg/ml) (12) to the lysozyme-EDTA solution to lyse the organism. Plasmid DNA was isolated from a chloramphenicol-amplified culture (18) of E. coli by the method of Bimboim and Doly (1) and then purified by gel filtration. A. faecalis Ti DNA was partially digested with Sau3AI, and fragments of 4 to 9 kilobase pairs (kbp) in size were isolated from the agarose gel by the glass powder method (28). The size-fractionated DNAs were ligated into BamHI-digested and alkaline phosphatase-treated pUC8, using T4 ligase. E. coli DH1 was transformed with recombinant plasmid DNA by the calcium chloride method of Mandel and Higa (17), and ampicillinresistant (Apr) transformants were selected and immunologically screened (9) with anti-PHB depolymerase immunoglobulin G raised in a rabbit.Restriction mapping and subcloning. Mapping of restriction sites was performed by the standard procedure (18). Deletion derivatives were constructed by digesting plasmids with a single restriction enzyme, followed by ligation of the products. Subcloning was performed by isolating DNA fragments from 0.8% agarose gels by electroelution onto DEAE-paper (6). These fragments were then ligated into pUC8 that had been cut with appropriate restriction enzymes. pUC8 with subcloned DNA fragments was introduced into the E. coli JM103 recipient by transformation, and white colonies containing recombinant plasmids were 184 JOURNAL
Extracts of normal mature articular cartilage contain aggrecan molecules which bear the G1 domain (the N-terminal globular domain of aggrecan) and are C-terminally truncated by proteolysis at a number of sites. A proportion of these molecules are generated by an aggrecanase and/or matrix-metalloproteinase-mediated cleavage in the IGD (interglobular domain between the G1 and G2 domains of aggrecan). However, the proteinase(s) responsible for formation of the majority of the larger G1-G2 and glycosaminoglycan-bearing truncated species is (are) unknown. N-terminal sequencing of aggrecan core fragments generated by m-calpain digestion of bovine aggrecan has identified four novel cleavage sites: one within the CS (chondroitin sulphate)-1 domain (at one or more of the bonds Ser1229-Val1230, Ser1249-Val1250, Ser1287-Val1288, Gly1307-Val1308 and Ser1346-Val1347), two within the IGD (at bonds Ala474-Ala475 and Gly365-Gly366) and one within the KS (keratan sulphate) domain (at Ala719-Ala720). A new monoclonal antibody (SK-28) to the C-terminal neoepitope at M710VTQVGPGVA719 showed that aggrecan products generated by this cleavage are present in high abundance in mature bovine articular cartilage extracts. We conclude that m-calpain, or an unidentified proteinase with the capacity to cleave at the same site, is active during aggrecan biosynthesis/secretion by mature chondrocytes or in the matrix of mature bovine articular cartilage in vivo.
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