Cloning and functional characterization of the chicken c-ros promoter.

Our previous study has shown that chicken c-ros is specifically expressed in certain epithelial cells of kidney, intestine, lung, bursa, thymus, and testis, and the expression is regulated temporally and spatially. To explore the molecular basis for the regulation of c-ros expression, we have cloned and characterized the chicken c-ros promoter. The most 5' c-ros cDNA was isolated and sequenced. Using the 5' cDNA as a probe, three genomic DNA clones containing the 5' c-ros cDNA sequence were isolated. Primer extension and RNase protection analysis were used to map the transcription initiation site for the c-ros mRNA in kidney and intestine. The sequence of the 1.3-kb region upstream of the initiation site contains TATA and CAAT boxes at 26 and 54 nucleotides, respectively, upstream of the initiation site. In addition, transcription factor binding sites for AP1, AP2, and Oct1 and several direct and inverted repeats are present within 1 kb upstream of the initiation site. The 1.3-kb DNA, when placed upstream of the chloramphenicol acetyltransferase gene, was shown to be functionally active. Serial deletions of this putative c-ros promoter allowed us to define a minimum c-ros promoter and to identify positive and negative regulatory regions. Using two oligonucleotides corresponding to a positive regulatory and potential factor binding region, we have demonstrated, by gel mobility shift experiments, their specific binding to nuclear extracts from kidney, intestine, and thymus. The binding pattern corresponds to the tissue specificity and temporal control of c-ros mRNA expression.