Regulation of alpha o expression by the 5'-flanking region of the alpha o gene.
Many responses of cells to external signals require activation of the heterotrimeric G proteins. These responses depend on the type and amount of G proteins that are expressed. Each cell has a characteristic complement of G protein subunits. For example, the alpha o subunit is very abundant in neural tissues. Very little is known about the mechanisms that determine cellular levels of G proteins. In the present study, we have isolated a genomic clone for mouse alpha o gene and identified the promoter region. There are multiple transcription initiation sites located about 750 base pairs upstream of the translational start site. The promoter region is GC-rich and contains neither a TATA-box nor a CAAT box. Transient expression assays using a series of constructs containing various lengths of the 5'-flanking region of the alpha o promoter demonstrated that the region 300-700 base pairs upstream of the transcription initiation sites is responsible for the basic promoter activity. The relative activity of alpha o promoter is 8-12-fold higher in cells expressing alpha o than in cells lacking alpha o. The level of alpha o in cells may also be regulated at the level of protein translation because deletions in the 5'-noncoding region of alpha o gene increase reporter enzyme expression without a corresponding increase in reporter enzyme mRNA level. Our results suggest that both transcriptional and post-transcriptional mechanisms are involved in regulating the expression of alpha o in vivo. Transcriptional regulation probably is important for control of tissue-specific expression, while posttranscriptional mechanisms may be used to regulate the alpha o level in cells.
Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115.
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Y
Li
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Mortensen
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Neer
D000818:Animals; D001483:Base Sequence; D019204:GTP-Binding Proteins / Q000235:genetics*; D005786:Gene Expression Regulation; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000235:genetics; D015183:Restriction Mapping; D016415:Sequence Alignment; D017384:Sequence Deletion; D012689:Sequence Homology, Nucleic Acid
D012333:RNA, Messenger; D019204:GTP-Binding Proteins