Rat pulmonary surfactant protein A is expressed as two differently sized mRNA species which arise from differential polyadenylation of one transcript.

In rat, the surfactant-associated glycoprotein A, SP-A, is encoded by two mRNA species of 0.9 and 1.6 kb. Each transcript is polyadenylated and is found in approximately the same ratio in total cellular RNA isolated from either alveolar type II cells or from whole lung. The two mRNA species have identical coding regions and differ only in the length of the 3' untranslated sequences. Restriction analysis and partial sequence analysis of rat genomic clones indicate that each mRNA species arises from one gene, with the difference in size most easily accounted for by differential polyadenylation. During fetal development, the accumulation of mRNA encoding SP-A is detectable by day 18 but increases many-fold on day 19. However, there are no apparent alterations in the prevalence of either mRNA species during fetal development or in the early postnatal period.