Fault-Tolerance Study on a Positive-Charged Cleft in 18S rRNA Methyltransferase DIMT1

Area of Science:

• Molecular Biology
• Cell Biology
• Biochemistry

Background:

• Dimethyladenosine transferase 1 (DIMT1) is crucial for pre-ribosomal RNA (pre-rRNA) processing and ribosome biogenesis.
• DIMT1's function is vital for maintaining cellular proliferation.

Purpose of the Study:

• To determine the minimal number of residues in DIMT1's positively charged cleft essential for cell proliferation.
• To investigate how mutations in this region affect DIMT1's RNA-binding ability and cellular localization.

Main Methods:

• Site-directed mutagenesis was used to create DIMT1 variants with altered residues in the positively charged cleft.
• RNA-binding affinity was assessed for wild-type and mutant DIMT1.
• Cellular localization of DIMT1 variants was examined using microscopy.
• Competition-based cell proliferation assays were performed to evaluate the functional impact of mutations.

Main Results:

• A minimum of four mutations in the positively charged cleft were required to significantly reduce DIMT1's RNA-binding affinity.
• The quadruple mutant (4mutA-DIMT1) exhibited reduced RNA binding and altered localization, becoming diffuse in the nucleoplasm and nucleolus.
• Wild-type DIMT1 predominantly localized to the nucleolus.
• The aberrant localization of 4mutA-DIMT1 impaired its ability to support cell proliferation.

Conclusions:

• The positively charged cleft of DIMT1 contains a minimal region of four residues critical for its RNA-binding function.
• Disruption of this region affects DIMT1's cellular localization and consequently impairs its role in ribosome biogenesis and cell proliferation.
• Targeting this specific region of DIMT1 offers a potential strategy for regulating cell proliferation.