Gene products of Amphiuma: An amphibian with an excessive amount of DNA

The nuclei of Amphiuma contain 168 pg of DNA, 28 times that contained in human nuclei. Although many higher organisms appear to possess an excessive amount of DNA, in Amphiuma this has been carried to the extreme. Studies of this organism thus may provide some insight into how this excess DNA is used. This organism presumably evolved by numerous polyploidy and gene duplication events. Do its gene products present multiple electrophoretic forms? Are they quantitatively increased to the same degree as the DNA? Electrophoresis of Amphiuma glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, acid phosphatase, lactic dehydrogenase, and hemoglobin failed to show any evidence for multiple electrophoretic forms of these respective gene products. The amount of hemoglobin, G6PD, and 6PGD per red cell was increased to a comparable or even greater degree than the DNA. Analytical ultracentrifugation demonstrated a satellite band of DNA with a density of 1.720 corresponding to a GC content of 61%. This probably represents DNA coding for ribosomal RNA. Electron microscopy of liver nuclei showed a significant amount of condensed chromatin. The implications of these observations are discussed.