Required for RNA polymerase III-mediated transcription. Component of TFIIIC that initiates transcription complex assembly on tRNA and is required for transcription of 5S rRNA and other stable nuclear and cytoplasmic RNAs. May play a direct role in stabilizing interactions of TFIIIC2 with TFIIIC1 (By similarity). Part of the TFIIIC subcomplex TFIIIC2, consisting of six subunits, GTF3C1, GTF3C2, GTF3C3, GTF3C4, GTF3C5 and GTF3C6. Intron retention.