A model of miRNA regulation mediated by SRF and its cofactors, including myocardin, p49/Strap, Zipzap and other proteins. Generally, the pri-miRNA transcript contains one miRNA (e.g pri-mir-21), but it can also contain more than one miRNAs (e.g. mir-1 and mir-133a). SRF regulates the transcription activity of both types of pri-miRNAs, thereby affecting the downstream mature miRNA level. The length of three representative primary transcripts: pri-mir-21 is over 3 kb, "pri-mir-1-1 and pri-mir-133a2" is 10 kb, and "pri-mir-1-2 and pri-mir-133a1" is 6 kb.