cDNA cloning of ovine pulmonary SP-A, SP-B, and SP-C: isolation of two different sequences for SP-B

Pulmonary surfactant promotes alveolar stability by lowering the surface te nsion at the air-liquid interface in the peripheral air spaces. The three s urfactant proteins SP-A, SP-B, and SP-C contribute to dynamic surface prope rties involved during respiration. We have cloned and sequenced the complet e cDNAs for ovine SP-A and SP-C and two distinct forms of ovine SP-B cDNAs. The nucleotide sequence of ovine SP-A cDNA consists of 1,901 bp and encode s a protein of 248 amino acids. Ovine SP-C cDNA contains 809 bp, predicting a protein of 190 amino acids. Ovine SP-B is encoded by two mRNA species, w hich differ by a 69-bp in-frame deletion in the region coding for the activ e airway protein. The larger SP-B cDNA comprises 1,660 bp, encoding a putat ive protein of 374 amino acids. With the sequences reported, a more complet e analysis of surfactant regulation and the determination of their physiolo gical function in vivo will be enabled.