Non-catalytic component of the METTL1-WDR4 methyltransferase complex required for the formation of N(7)-methylguanine in a subset of RNA species, such as tRNAs, mRNAs and microRNAs (miRNAs) (PubMed:12403464, PubMed:31031083, PubMed:31031084, PubMed:36599982, PubMed:36599985, PubMed:37369656). In the METTL1-WDR4 methyltransferase complex, WDR4 acts as a scaffold for tRNA-binding (PubMed:36599982, PubMed:36599985, PubMed:37369656). Required for the formation of N(7)- methylguanine at position 46 (m7G46) in a large subset of tRNAs that contain the 5'-RAGGU-3' motif within the variable loop (PubMed:12403464, PubMed:34352206, PubMed:34352207, PubMed:36599982, PubMed:36599985, PubMed:37369656). M7G46 interacts with C13-G22 in the D-loop to stabilize tRNA tertiary structure and protect tRNAs from decay (PubMed:36599982, PubMed:36599985). Also required for the formation of N(7)-methylguanine at internal sites in a subset of mRNAs (PubMed:31031084, PubMed:37379838). Also required for methylation of a specific subset of miRNAs, such as let-7 (PubMed:31031083). Independently of METTL1, also plays a role in genome stability: localizes at the DNA replication site and regulates endonucleolytic activities of FEN1 (PubMed:26751069). {ECO:0000269|PubMed:12403464, ECO:0000269|PubMed:26751069, ECO:0000269|PubMed:31031083, ECO:0000269|PubMed:31031084, ECO:0000269|PubMed:34352206, ECO:0000269|PubMed:34352207, ECO:0000269|PubMed:36599982, ECO:0000269|PubMed:36599985, ECO:0000269|PubMed:37369656, ECO:0000269|PubMed:37379838}. This is the function of WDR4 (WDR4 tRNA N7-guanosine methyltransferase non-catalytic subunit, Ensembl gene identifier ENSG00000160193).