Sequence of a cDNA encoding turtle riboflavin-binding protein: a comparison with avian riboflavin-binding protein.
To search for the existence and distribution of a riboflavin-binding protein (RfBP), total RNA from estrogen-treated oviparous animals were screened by Northern hybridization using chicken RfBP cDNA as a probe. Besides avian livers and oviducts, RfBP mRNA was found in turtle liver, but not in the turtle oviduct. To elucidate the structure of the RfBP from a reptilian source, we constructed a cDNA library from estrogen-injected turtle liver, and a full-length turtle RfBP-encoding cDNA was cloned and sequenced. The open reading frame (ORF) encoded 242 amino acids (aa) including a signal peptide of 18 aa. There is an overall 71.3% aa identity between the deduced aa sequences of turtle and chicken. The aa sequence of turtle and chicken RfBP also show more than 30% similarity to a fragment of folate-binding protein (FBP). Six Trp and nine pairs of Cys residues are conserved between the two RfBPs with only one pair of Cys residues missing in FBP. The two Asn-linked glycosylation sites found in chicken RfBP are conserved in turtle RfBP, but only one of which is conserved in FBP. However, there is an additional potential N-glycosylation site in the turtle sequence and this may provide a better explanation for the greater molecular weight of the turtle protein than chicken RfBP. Turtle RfBP contains a region of nine Ser and five Glu residues which is present in mature chicken RfBP as eight phosphorylserine clusters forming a highly anionic region at the C terminus, but this region is not found in FBP.
Hamajima
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Department of Biochemistry, School of Medicine, Iwate Medical University, Morioka, Japan.
Ono
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D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000096:biosynthesis / Q000235:genetics*; D002645:Chickens / Q000235:genetics*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D004967:Estrogens / Q000494:pharmacology; D015723:Gene Library; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D026901:Membrane Transport Proteins; D008969:Molecular Sequence Data; D016366:Open Reading Frames; D010057:Oviducts / Q000378:metabolism; D021382:Protein Sorting Signals / Q000096:biosynthesis / Q000235:genetics; D012333:RNA, Messenger / Q000032:analysis / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D014426:Turtles / Q000235:genetics*
D002352:Carrier Proteins; D018076:DNA, Complementary; D004967:Estrogens; D026901:Membrane Transport Proteins; D021382:Protein Sorting Signals; D012333:RNA, Messenger; D011994:Recombinant Proteins; C019079:riboflavin-binding protein