Abstract. Type II collagen is a major component of cartilage providing structural integrity to the tissue. Type II procollagen can be expressed in two forms by differential splicing of the primary gene transcript. The two mRNAs either include (type IIA) or exclude (type IIB) an exon (exon 2) encoding the major portion of the amino (NH2)-propeptide (Ryan, M. C., and L. J. Sandell . 1990. J. Biol. Chem. 265 :10334-10339) . The expression of the two procollagens was examined in order to establish a potential functional significance for the two type II procollagen mRNAs . First, to establish whether the two mRNAs are functional, we showed that both mRNAs can be translated and the proteins secreted into the extracellular environment . Both proteins were identified as type II procollagens . Secondly, to test the hypothesis that differential expression of type II procollagens may be a marker for a distinct population of cells, specific procollagen mRNAs were localized in tissue by in situ hybridization to oligonucleotides spanning the exon junctions . Embryonic vertebral column was chosen as a source of tissue undergoing rapid chondrogenesis, allowing the examination of a variety of cell types related to cartilage . In this issue, each procollagen mRNA had a distinct tissue distribution during chondrogenesis with type IIB expressed in chondrocytes and type IIA ex-YPE II collagen is the predominant collagenous component of cartilage composing >50 % of the extracellular matrix . Like type I collagen, the most abundant col lagen in vertebral organisms, it is an interstitial collagen' synthesized as a procollagen monomer, assembled into molecular trimers and processed extracellularly to remove NH2-and COON-terminal extension propeptides . The interstitial collagen monomer contains a non-interrupted Gly-XY protein domain of -1,014 amino acids, flanked by the globular propeptides . The COOH-terminal propeptide of ti 275 amino acids is connected to the main triple helix by a short telopeptide, is highly conserved between interstitial collagens, and is thought to be involved in initiation of trimer formation .The NH2-terminal propeptide shows more structural and sequence diversity among the interstitial collagens, but generally consists of a short globular domain followed by a cysteine-rich domain, a Gly-XY domain of40-60 residues, and a short connecting telopeptide (Sandell and Boyd, 1990) . It
The chemical basis for the alternating antigenic change called form variation noted for the Escherichia coli K1-capsular polysaccharide has been shown by 13C nuclear magnetic resonance to be a result of random O-acetylation of C7 and C9 carbons of the alpha-2-8-linked sialic acid homopolymer. A serologic method (antiserum agar) was developed to identify and isolate the form variants. The O-acetyl positive and O-acetyl negative K1 polysaccharides had unique biochemical and immunologic properties. The O-acetyl-positive variants resisted neuraminidase hydrolysis in contrast to the susceptibility of the O-acetyl negative variant to this enzyme. In addition, O-acetylation altered the antigenicity of the O-acetyl polysaccharides. When injected as whole organisms, O-acetyl positive organisms produced anti-K1 -antibodies in rabbits specific for this polysaccharide variant. O-acetyl negative organisms were comparatively less immunogenic; however, antibodies induced by these organisms reacted with both K1 polysaccharide variants. Burros, injected with either variant, produced antibodies reactive with both K1 polysaccharides.
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