Molecular cloning and primary structure of rat thyroxine-binding globulin.
Rat thyroxine-binding globulin (TBG) cDNAs were isolated from a rat liver cDNA library by using a human TBG cDNA as a probe. From two overlapping cDNA inserts, an aligned cDNA sequence of 1714 nucleotides was obtained. There was 70% homology with human TBG cDNA over the span of 1526 nucleotides. In order to confirm that the cloned cDNA encodes rat TBG and to localize the NH2-terminal amino acid of the mature molecule, the protein was purified by affinity chromatography and subjected to direct protein microsequencing. The NH2-terminal amino acid sequence was identical with that deduced from the nucleotide sequence. The rat TBG cDNA sequenced consisted of a truncated leader sequence (35 nucleotides), the complete sequence encoding the mature protein (1194 nucleotides) and the 3'-untranslated region (485 nucleotides), containing two polyadenylation signals. It was deduced that rat TBG consists of 398 amino acids (Mr = 44,607), three NH2-terminal residues more than human TBG, with which it shares 76% homology in primary structure. Of the six potential N-glycosylation sites, four are located in conserved positions compared to human TBG. Northern blot analysis of rat liver revealed an approximately 1.8-kilobase TBG mRNA. Its amount increased markedly following thyroidectomy and decreased with thyroxine treatment in a dose-dependent manner.
Imamura
S
S
First Department of Internal Medicine, Nagoya University School of Medicine, Japan.
Mori
Y
Y
Murata
Y
Y
Yamamori
I
I
Miura
Y
Y
Oiso
Y
Y
Seo
H
H
Matsui
N
N
Refetoff
S
S
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000737:chemistry; D015342:DNA Probes; D015870:Gene Expression / Q000187:drug effects; D006031:Glycosylation; D006801:Humans; D008099:Liver / Q000737:chemistry; D008297:Male; D008969:Molecular Sequence Data; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D013974:Thyroxine / Q000494:pharmacology; D013975:Thyroxine-Binding Proteins / Q000737:chemistry* / Q000235:genetics
D015342:DNA Probes; D012333:RNA, Messenger; D013975:Thyroxine-Binding Proteins; D004247:DNA; D013974:Thyroxine