Characterization of a Second Human Pulmonary Surfactant-associated Protein SP-A Gene

Pulmonary surfactant is a lipid-protein complex involved in maintaining alveolar stability. SP-A is the major surfactant-associated protein of 26 to 38 kD. A human SP-A gene (SP-A I) and two distinct SP-A cDNAs, MPSAP 1A and MPSAP 6A, have been reported previously. We have isolated and characterized a second human SP-A gene (SP-A II), which appears to code for the mRNA corresponding to the previously described MPSAP-1A cDNA. Both genes consist of five exons, a consensus recognition sequence for initiation, TATAAA, and a polyadenylation signal sequence. Significant divergence in the two genes is observed throughout. The divergence is highest in the upstream region, intron I, exon III, and noncoding portion of exon V. The coding regions of all other exons and the introns show much lower divergence. Transcripts from both genes were found in adult human lung, using gene-specific oligonucleotide probes in Northern blot analysis.