Analysis of the 5'-flanking regions of rat inhibin alpha- and beta-B-subunit genes suggests two different regulatory mechanisms.

The genes encoding rat inhibin alpha- and beta-B-subunits were isolated and characterized. Both genes contain one intron that interrupts the region coding for the precursor portion of the alpha- and beta-B-subunits. The transcription start sites of alpha- and beta-B-subunit genes were determined by primer extension and nuclease mapping assay using mRNA from rat ovary and testis. Transcription of the alpha-subunit gene initiates predominantly at three adjacent sites with similar intensity. Several potential transcription start sites of beta-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 alpha-subunit gene contains many GA clusters in the promoter region, while beta-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 beta-B-subunit gene. The potential cAMP-responsive element CTGCGTCAG was identified in alpha-but not beta-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 alpha- and beta-B-subunit genes and the presence of a potential cAMP-inducible DNA sequence in alpha- but not beta-B-subunit gene is consistent with the hypothesis that transcription of alpha- and beta-B-subunit genes in rat is regulated by different mechanisms.