Identification of alternative first exons of NADH-cytochrome b5 reductase gene expressed ubiquitously in human cells.
Two forms of NADH-cytochrome b5 reductase (b5R), soluble and membrane-bound, are known. A hypothesis that the human soluble form b5R is generated through post-translational processing of the membrane-bound form was previously proposed. In this study, the 5'-rapid amplification of cDNA ends for human reticulocyte, liver, brain, and HL-60 cell mRNAs revealed the ubiquitous presence of an alternative type of human b5R mRNA which can probably be translated into the soluble form b5R directly; however, the erythroid-specific transcript of the b5R gene was not found. This type of b5R mRNA initiating from at least two sites contains a non-coding new first exon located between the first two exons of the human b5R gene identified before. In addition, this new first exon shares 62% homology with the first exon and its 3'-flanking intron sequences of rat erythroid-specific b5R mRNA, whereas the 5'-flanking region of the new first exon possesses features of house-keeping gene. These results might be important to understand the regulation mechanism of human b5R biosynthesis and divergent evolution of the gene regulation.
Du
M
M
Department of Biochemistry, Oita Medical University, Japan.
Shirabe
K
K
Takeshita
M
M
D000818:Animals; D001483:Base Sequence; D001921:Brain / Q000201:enzymology; D003579:Cytochrome Reductases / Q000096:biosynthesis* / Q000235:genetics*; D042966:Cytochrome-B(5) Reductase; D017931:DNA Primers; D005091:Exons; D018922:HL-60 Cells / Q000201:enzymology; D006801:Humans; D008099:Liver / Q000201:enzymology; D008969:Molecular Sequence Data; D009928:Organ Specificity; D016133:Polymerase Chain Reaction; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis; D051381:Rats; D012156:Reticulocytes / Q000201:enzymology; D014158:Transcription, Genetic
D017931:DNA Primers; D012333:RNA, Messenger; D003579:Cytochrome Reductases; D042966:Cytochrome-B(5) Reductase