Predicted to enable ATP binding activity; mRNA 5'-triphosphate monophosphatase activity; and mRNA guanylyltransferase activity. Predicted to be involved in 7-methylguanosine mRNA capping. Is an ortholog of C. elegans cel-1. In C. elegans, cel-1 is involved in polynucleotide 5' dephosphorylation and positive regulation of gene expression.