The myotonic dystrophy type 2 protein ZNF9/CNBP is a small nucleic acid binding protein proposed to act as a regulator of transcription and translation. The precise functions and activity of this protein are poorly understood. Previous studies suggested that ZNF9 regulates translation and facilitates the process of cap-independent translation through interactions with mRNA and the translating ribosome. To help determine the role played by ZNF9 in the activation of translation initiation, we combined genetic and biochemical analysis of the putative ZNF9 ortholog GIS2, in the budding yeast Saccharomyces cerevisiae. Purification of the Gis2p protein followed by mass spectrometry based-proteomic analysis identified a large number of co-purifying ribosomal subunits and translation factors, strongly suggesting that Gis2p interacts with the protein translation machinery. Polysome profiling and ribosome isolation experiments confirm that Gis2p physically interacts with the translating ribosome. Interestingly, expression of yeast Gis2p in HEK293T cells activates cap-independent translation driven by the 5'UTR of the ODC gene. These data suggest that Gis2 is functionally orthologous to ZNF9 and acts as a cap-independent translation factor.
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