title: The gene G13 in the class III region of the human MHC encodes a potential DNA-binding protein.
abstract: G13 is a single-copy gene lying approx. 75 kb centromeric of the complement gene cluster in the class III region of the human MHC. The gene spans approx. 17 kb of DNA and has been shown to encode mRNA of approx. 2.7 kb that is present in cell lines representing lymphoid and non-lymphoid tissues, indicating that it is ubiquitously expressed. The complete nucleotide sequence of the 2.7 kb mRNA has been derived from cDNA and genomic clones. The longest open reading frame obtained for G13 codes for a 703 amino acid protein of approx. 77 kDa in molecular mass. Comparison of the putative G13 amino acid sequence with the protein databases revealed significant similarities with DNA-binding proteins of the leucine zipper class, including a human cAMP response element binding protein. G13 contains a bZIP motif, a region rich in basic amino acids adjacent to a coiled-coil leucine zipper domain, common to this class of proteins that is known to be involved in dimerization and DNA binding. Antibodies raised against a fragment encoding the C-terminal half of the putative G13 protein recognized a major polypeptide of approx. 86 kDa and a minor polypeptide of approx. 78 kDa on immunoblotting of U937 cell extracts; this has been confirmed by immunoprecipitation experiments. Even though it contained at least one potential bipartite nuclear localization signal, the G13 protein was present both in the cytoplasm and the nucleus of the fibroblast cells. Thus G13 might be a novel DNA-binding protein that is perhaps translocated to the nucleus in a regulated manner.
authors.affiliation: Department of Biochemistry, University of Oxford, U.K.
authors.forename: A
authors.initials: A
authors.lastname: Khanna
authors.forename: R D
authors.initials: RD
authors.lastname: Campbell
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D002460:Cell Line; D002874:Chromosome Mapping; D002896:Chromosomes, Human, Pair 6; D017362:Cyclic AMP Response Element-Binding Protein / Q000737:chemistry / Q000235:genetics; D018076:DNA, Complementary / Q000302:isolation & purification; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics*; D051790:G-Box Binding Factors; D044365:GTP-Binding Protein alpha Subunits, G12-G13; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007544:Isopropyl Thiogalactoside / Q000494:pharmacology; D016350:Leucine Zippers; D008285:Major Histocompatibility Complex; D008969:Molecular Sequence Data; D008970:Molecular Weight; D015183:Restriction Mapping; D017422:Sequence Analysis, DNA; D014157:Transcription Factors
chemical_list: D050976:Basic-Leucine Zipper Transcription Factors; D017362:Cyclic AMP Response Element-Binding Protein; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D051790:G-Box Binding Factors; D014157:Transcription Factors; D007544:Isopropyl Thiogalactoside; D044365:GTP-Binding Protein alpha Subunits, G12-G13