MicroRNAs (miRNAs) are short non-coding RNAs that play essential roles in RNA silencing and gene regulation. The human Microprocessor is the key factor to initiate miRNA biogenesis by cleaving primary microRNA (pri-miRNA). However, the Microprocessor cannot precisely and efficiently process all types of pri-miRNAs; thus, its cofactors assistance is required. SRSF3, a member of the serine/arginine-rich splicing factor family (SR proteins family), is one of the Microprocessor cofactors. By interacting with the CNNC motif in the 3p flanking region of pri-miRNAs, SRSF3 enhances the accuracy and efficiency of Microprocessor cleavage activity. However, the functions of SRSF7 (paralog of SRSF3 in the SR proteins family) in miRNA biogenesis have not been established yet. In this study, we condu...[ Read more ]

MicroRNAs (miRNAs) are short non-coding RNAs that play essential roles in RNA silencing and gene regulation. The human Microprocessor is the key factor to initiate miRNA biogenesis by cleaving primary microRNA (pri-miRNA). However, the Microprocessor cannot precisely and efficiently process all types of pri-miRNAs; thus, its cofactors assistance is required. SRSF3, a member of the serine/arginine-rich splicing factor family (SR proteins family), is one of the Microprocessor cofactors. By interacting with the CNNC motif in the 3p flanking region of pri-miRNAs, SRSF3 enhances the accuracy and efficiency of Microprocessor cleavage activity. However, the functions of SRSF7 (paralog of SRSF3 in the SR proteins family) in miRNA biogenesis have not been established yet. In this study, we conducted the cleavage assay of the Microprocessor with and without SRSF3 or SRSF7 on pri-miRNAs. Interestingly, we found that SRSF3 and SRSF7 changed the cleavage sites of the Microprocessor complex on several pri-miRNAs such as pri-mir-142. However, these two factors had differential activity on different CNNC-pri-miRNAs. We have also conducted the high-throughput pri-miRNA processing cleavage assays using thousands of pri-miRNA variants with Microprocessor and SRSF7. The high-throughput data revealed the critical RNA motif and secondary structures that are required for the functions of SRSF7. In addition, we also demonstrated that SRSF7 governed the cleavage sites of the Microprocessor on pri-mir-142 in human cells. Our findings disclose the roles of SRSF7 in miRNA biogenesis and its substrate features, expanding our understanding of pri-miRNA processing mechanisms.