Organization of the human SP-A and SP-D loci at 10q22-q23. Physical and radiation hybrid mapping reveal gene order and orientation.

The human surfactant protein (SP) A locus has been assigned to chromosome 10q22-q23 and consists of two very similar genes, SP-A1 and SP-A2, as well as a truncated pseudogene. SP-A belongs to the family of collagenous C-type lectins along with mannose binding protein (MBP) and SP-D, both of which have also been mapped to the long arm of chromosome 10. In this article we report the relative location and orientation of each of the SP-A and SP-D genomic sequences. Characterization of two overlapping genomic clones revealed that the SP-A pseudogene lies in a reverse orientation 15 kb away from the 5' side of SP-A1. This finding was verified by the amplification of the entire SP-A pseudogene/SP-A1 intergenic region using long-range polymerase chain reaction. The relative location of SP-A2 and SP-D was then ascertained by testing a number of sequence tagged sites against the Stanford TNG3 and G3 radiation hybrid panels. The radiation hybrid mapping data showed that both SP-A2 and SP-D are on the 5' side of SP-A1 at approximate distances of 40 kb and 120 kb, respectively. The SP-A and SP-D loci were also oriented relative to the centromere, with the overall order being: centromere-SP-D-SP-A2-pseudogene-SP-A1- telomere.