Analysis of the 5′-Flanking Regions of Rat Inhibin α- and β-B-Subunit Genes Suggests Two Different Regulatory Mechanisms

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Abstract
The genes encoding rat inhibin α- and β-B-subunits were isolated and characterized. Both genes contain one intron that interrupts the region coding for the precursor portion of the α- and β-B-subunits. The transcription start sites of α- and β-B-subunit genes were determined by primer extension and nuclease mapping assay using mRNA from rat ovary and testis. Transcription of the α-subunit gene initiates predominantly at three adjacent sites with similar intensity. Several potential transcription start sites of β-B-subunit gene are spread over 150 nucleotides upstream from translation initiation site. Neither of these two genes contains obvious TATA or CCAAT boxes. The α-subunit gene contains many GA clusters in the promoter region, while β-B-subunit gene is highly GC rich. Several GGGCGG repeats and their inverted sequences, which are the potential binding sites for transcription factor Spl, were observed at the 5′-end as well as at the coding region of the β-B-subunit gene. The potential cAMP-responsive element CTGCGTCAG was identified in α- but not β-B-subunit gene. This sequence is identical to the cAMP- and phorbol ester-inducible DNA fragment found in human preproenkephalin gene. The different structure of the promoter region of rat α- and β-B-subunit genes and the presence of a potential cAMP-inducible DNA sequence in α- but not β-B-subunit gene is consistent with the hypothesis that transcription of α- and β-B-subunit genes in rat is regulated by different mechanisms.