Regulatory subunit of the mRNA-capping methyltransferase RNMT:RAMAC complex that methylates the N7 position of the added guanosine to the 5'-cap structure of mRNAs (PubMed:22099306, PubMed:27422871). Promotes the recruitment of the methyl donor, S- adenosyl-L-methionine, to RNMT (PubMed:27422871). Regulates RNMT expression by a post-transcriptional stabilizing mechanism (PubMed:22099306). Binds RNA (PubMed:22099306). . This is the function of ENSG00000169612 (RAMAC, RNA guanine-7 methyltransferase activating subunit).