ABSTRACT
Structural and functional similarities are frequently found among many proteins, and such resemblance often suggests common modes of action or regulation. However, the question that often remains unresolved is if such similar molecules are evolutionarily conserved to perform exactly similar and redundant functions, or if they have specific and different biological roles that have yet to be uncovered. One such family of proteins is the c-Jun-N-terminal (JNK) kinases that are present ubiquitously in the organism. The JNK sub group consists of three members-JNK1, JNK2 and JNK3-which are highly homologous and are present as multiple isoforms. Although combinatorial use of the various JNKs and their upstream kinases are thought to lead to differential regulation of various cellular processes, the specific roles of the JNK proteins were not clarified till the generation of the JNK mutant mice. This review will thus attempt to summarize the specific and redundant roles of JNK proteins, by analyzing the data obtained using the various JNK knockout mice.
