The Drosophila melanogaster DmCK2β transcription unit encodes for functionally non-redundant protein isoforms

Genes encoding for the two evolutionary highly conserved subunits of a heterotetrameric protein kinase CK2 holoenzyme are present in all examined eukaryotic genomes. Depending on the organism, multiple transcription units encoding for a catalytically active CK2α subunit and/or a regulatory CK2β subunit may exist. The phosphotransferase activity of members of the protein kinase CK2α family is thought to be independent of second messengers but is modulated by interaction with CK2β-like proteins. In the genome of Drosophila melanogaster, one gene encoding for a CK2α subunit and three genes encoding for CK2β-like proteins are present. The X-linked DmCK2β transcription unit encodes for several CK2β protein isoforms due to alternative splicing of its primary transcript. We addressed the question whether CK2β-like proteins are redundant in function. Our in vivo experiments show that variations of the very C-terminal tail of CK2β isoforms encoded by the X-linked DmCK2β transcription unit influence their functional properties. In addition, we find that CK2β-like proteins encoded by the autosomal D. melanogaster genes CK2βtes and CK2β′ cannot fully substitute for a loss of CK2β isoforms encoded by DmCK2β.