Gene (Rmmp1) of matrix metalloproteinase 1 (MMP1) of the bullfrog, Rana catesbeiana, has been shown previously to contain a thyroid hormone response element (TRE)-like sequence in its 5'-upstream region. The present study aimed to determine whether this TRE-like sequence is functional in vivo as a true TRE, and to characterize the sequences of the 5'-upstream region with respect to the regulation of the activity of the TRE when the TRE-like sequence was proved to be a true TRE. With this aim, various sequences of TRE-like sequence-containing 5'-upstream region were constructed and fused to the enhanced green fluorescent protein gene as a reporter gene. The fusion constructs were bombarded to the skin of bullfrog tadpoles and the activity of the TRE was quantitatively determined by measuring increased intensities of fluorescence when the animals were exposed to thyroid hormone. The present study clearly demonstrated that the sequence of Rmmp1 is a biologically active TRE in vivo. In addition, a unique 36 bp long sequence directly flanked to the 3'-end of the TRE was identified which worked co-operatively with TRE to regulate the transcriptional promoter activity. It should be emphasized that the presence of TRE in the Rmmp1 gene is unique, because its presence has not been reported in the known promoter region of vertebrate MMPs.

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