Molecular cloning of three genes encoding SNF1/AMPK protein kinases from Drosophila melanogaster.

A number of different genes are known to play a role in the yeast glucose repression pathway and the SNF1 gene, encoding a serine-threonine protein kinase, has the essential function of releasing genes from glucose repression in response to glucose starvation. SNF1 homologues have been found in a number of different organisms and recent molecular and biochemical evidence has revealed that the mammalian AMP-activated protein kinases (AMPKs), known to regulate fatty acid and sterol metabolism in response to stress, represent the mammalian homologues of SNF1. Three novel Drosophila protein kinases were cloned and found to represent homologues of previously reported protein kinases. Two of the Drosophila protein kinase genes reported here, DM_SNF1B-1 and DM_SNF1B-2 are found clustered in tandem within a 4-kb region of the Drosophila genome. The encoded polypeptides share intermediate levels of sequence similarity with SNF1 but share higher levels of sequence similarity with the putative human protein kinase KP78, a marker protein lost in chemically induced primary carcinoma of the pancreas. The third Drosophila protein kinase gene DM_SNF1A , which is found in a single copy in the Drosophila genome, was found to share high similarity with the yeast SNF1 and an even higher level of similarity (92% similarity within the catalytic domain) with the mammalian AMPKs. Although the non-catalytic regulatory domain of Dm_snf1 a contains a number of features held in common with the two mammalian Ampk-alpha isoforms, it also contains features held in common with yeast Snf1 and which are missing in the Ampk-alpha isoforms. Some of these features may be the basis for known functional differences between the yeast and mammalian kinases. In addition to well-established SNF1 homologues, a growing number of "SNF1-related" kinase sequences exist in the various molecular sequence databases. Phylogenetic analysis of these sequences, along with those of the three novel kinases reported here, revealed that DM_SNF1A, is found on a well-supported branch that includes well-known SNF1-homologues. DM_SNF1B-1 and DM_SNF1B-2 branch along with kinases related to the human KP78 kinase. (Abstract shortened by UMI.