Conservation analysis of rat and human SP-A gene identifies 5' flanking sequences of rat SP-A that bind rat lung nuclear proteins.

As an initial step toward understanding regulation of tissue-specific expression of SP-A, 5' flanking sequences of the rat SP-A gene and human SP-A I gene were cloned, sequenced, and compared using dot matrix analysis. Two regions were identified, each with a considerable degree of homology between the two species. One region was proximal to the TATAA box, at position -225/-17 in rats and -226/-36 in humans, and the other at position -1115/-1026 in rats and -938/-851 in humans. Studies in rats revealed the specific binding of rat lung nuclear proteins to each of the conserved 5' flanking regions identified in rat SP-A. Binding studies using the rat proximal (rPPS) or distal (rDPS) promoter segments, or overlapping fragments of these segments, with rat nuclear extracts detected the presence of a number (1-4) of lung-specific DNA/protein complexes. When nuclear proteins from liver, a nonexpressing tissue, were used the binding profile of certain nuclear proteins differed from that of the lung. These studies, taken together, suggest that sequences within identified conserved DNA segments in the 5' flanking region of the rat SP-A gene contribute to its tissue-specific expression in rats.