ISOZYME PATTERNS OF SALMONID FISHES - EVIDENCE FOR MULTIPLE CISTRONS FOR LACTATE DEHYDROGENASE POLYPEPTIDES

Starch gel electrophoretic and molecular hybridization studies indicate that the genomes of rainbow (Salmo gairdneri) and brown (S. trutta) trouts may code for eight electrophoretically distinct types of lactate dehydrogenase (LDH) subunits. The interactions of these subunits in vivo produce eighteen isozymes. These isozymes are naturally arranged into four groups, designated a, b, d, and e, on the basis of physico‐chemical properties. Groups a, b, and d each consist of five isozymes while group e is composed of three isozymes. An obvious tissue specific distribution of the isozyme groups is observed. Like the rainbow and brown trouts, other salmonids such as the Atlantic salmon (S. salar), sockeye (Onchorynchus nerka), and bloater (Coregonus hoyi) possess numerous LDH isozymes. Also, we and others have detected an unusual multiplicity of molecular forms of other proteins in Salmonidae. Representatives of the Osmeridae, Clupeidae, Engraulidae, Argentidae, and Esocidae, which are closely related families, possess no more than five LDH isozymes. Moreover, salmonids contain twice as much DNA per cell and have karyotypes which show about twice as many chromosome arms as certain closely related forms. From these observations, it has been concluded that salmonids are tetraploids. In our view, it seems most likely that they arose through allotetraploidization of a primitive hybrid ancestor. Copyright © 1968 Wiley‐Liss, Inc., A Wiley Company