PSA-LM is secreted in serum, semen, and urine. His colleagues hope to further characterize the expression of PSA and its mate, and perhaps improve the current diagnostic test for prostate cancer by following levels of both proteins. And the existence of PSA-LM reveals one way in which a gene can be more than the sum of its parts. Plant scientists are also searching for genes within genes, but the small size of most plant introns makes this a difficult endeavor. Palmer agrees, but he cautions that small introns are probably the case in most organisms.
Researchers know of at least one gene within an intron in rice.
A functional rps14 gene encoding a mitochondrial ribosomal protein sits within an intron of another gene, for succinic dehydrogenase. Palmer points to genes within mobile introns still contained in mitochondria and chloroplasts. In the inherited condition dentinogenesis imperfecta, teeth are discolored, oddly shaped, and have peeling enamel. The problem stems from a protein unique to dentin, the bone-like substance beneath the enamel that forms the bulk of the tooth. Dentin is a complex mixture of extracellular matrix proteins, of which 90 percent is collagen.