Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.26.9 (ribonuclease)
 6,589 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Corneal proteoglycans have chondroitin/dermatan and keratan sulfate (KS) chains and belong to the leucine-rich proteoglycan gene family. Corneal KS is N-linked to Asn of an NX(S/T) site through a complex oligosaccharide linkage region. Only some sites receive KS, whereas others remain in a high mannose form. To determine whether the attachment of KS was biased toward specific sites, we isolated trypsin-digested KS-containing fragments of chick corneal proteoglycans and sequenced the peptides. Results showed that all of the peptides sequenced aligned to the deduced amino acid sequence of either chick lumican or chick keratocan at the first, third, and fourth potential N-linked sites. Sites 1 and 4 in lumican and keratocan are in a homologous location. By analogy with the structure of ribonuclease inhibitor (a Leu-rich repeat containing protein), the KS chains would extend outward on the outer face of a horseshoe-like structure. The amino acid sequences surrounding the potential N-linked sites were also compared. Sites receiving KS tend to have a higher occurrence of aromatic residues, in particular Phe, located within 3 amino acids of NX(S/T). These conserved Phe residues may have a role in the conversion of high mannose N-linked oligosaccharides to polylactosamine and/or keratan sulfate.
 ...
PMID:Identification of the N-linked oligosaccharide sites in chick corneal lumican and keratocan that receive keratan sulfate. 954 93

Mimecan is a proteoglycan expressed by many connective tissues. It was originally isolated in a truncated form as a bone-associated glycoprotein, osteoglycin, and was considered an osteoinductive factor. Recently, we demonstrated that the full-length translation product of the cDNA encoding mimecan is a corneal keratan sulfate proteoglycan present in other tissues without keratan sulfate chains. We also described multiple mimecan mRNA transcripts generated by differential splicing and alternative polyadenylation. In this study, we isolated genomic clones and determined the genomic organization of the bovine mimecan gene. The gene is spread over >33 kilobases of continuous DNA sequence and contains eight exons. The newly discovered first exon, identified by 5'-rapid amplification of cDNA ends, consists of a 5'-untranslated region and is enriched in C+G nucleotides. Two transcription initiation sites starting at the first and at the second exons were determined by primer extension. Molecular characterization shows that alternatively spliced RNA isoforms are generated by the use of two distinct splice acceptor sites in the third exon situated 278 base pairs apart. We determined a partial genomic structure of the human mimecan gene and demonstrated two alternatively spliced RNA transcripts that are generated likewise. Despite the diversity of mimecan transcripts, the primary structure of the core protein is encoded from exons 3 to 8 and remains unchanged, indicating its functional importance. Using ribonuclease protection assay, we analyzed the patterns of spliced RNA expressed in cultured bovine keratocytes. We demonstrated that their expression is differentially modulated in a temporal manner by basic fibroblast growth factor.
 ...
PMID:The bovine mimecan gene. Molecular cloning and characterization of two major RNA transcripts generated by alternative use of two splice acceptor sites in the third exon. 1037 82

Keratocan, along with lumican and mimecan, represent the keratan sulfate-containing proteoglycans of the vertebrate cornea that play a key role in development and maintenance of corneal transparency. In this study, we cloned 4.1 kb of the human Kera 5'-flanking region and characterized the promoter structure. Using primer extension and ribonuclease protection assay, we identify two major transcriptional start sites in the first exon. Using luciferase reporter gene transfection analysis of 5'-deletion and mutation constructs, we demonstrate positive and negative regulatory elements within a 1.3 kb upstream sequence. Comparison of human and bovine 5'-flanking sequences reveals three highly conserved regions: a 450 bp region in the first exon, a 92 bp promoter proximal conserved regulatory region identified as an enhancer in the natural context, and a 223 bp promoter distal conserved regulatory region identified as a silencer both in the natural context and in a heterologous promoter system. In addition, a conserved CArG-box residing 851 bp upstream of the first transcription start site also can lead to the repression of Kera expression in cultured corneal keratocytes. DNaseI footprinting and electrophoretic mobility shift assay demonstrate that cell type-specific factors bind to regulatory elements located in the conserved regions. Competition experiments indicate that the CTC factor and a protein that binds to the CAGA motif are likely to be among the multiple factors involved in the transcriptional regulation of the human Kera gene.
 ...
PMID:Identification and characterization of conserved cis-regulatory elements in the human keratocan gene promoter. 1089 81