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Distinct Functions of the Tor1 and Tor2 Kinases in Regulation of the Ribosomal Protein Gene Expression via TORC1, Not

Amala Kaja1, Bhawana Uprety1, Pritam Chakraborty1

  • 1Division of Biochemistry and Molecular Biology, Department of Biomedical Sciences, Southern Illinois University School of Medicine, Carbondale, Illinois, USA.

Molecular and Cellular Biology
|December 4, 2025
PubMed

Insights

Target of rapamycin (TOR) regulates ribosomal protein gene expression. Genetic analysis reveals Tor1 and Tor2 act redundantly via TORC1, not TORC2, for pre-initiation complex formation and transcription.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Genetics

Background:

  • The serine/threonine kinase, target of rapamycin (TOR), is crucial for cell growth and metabolism.
  • TOR functions in two distinct complexes, TORC1 and TORC2, with partially overlapping components.
  • Pharmacological inhibition of TOR by rapamycin affects pre-initiation complex (PIC) formation and ribosomal protein gene transcription.

Purpose of the Study:

  • To genetically elucidate the distinct roles of Tor1, Tor2, TORC1, and TORC2 in regulating ribosomal protein gene expression.
  • To investigate the involvement of TOR complexes in pre-initiation complex (PIC) formation and gene transcription.

Main Methods:

  • Gene knockout (null mutation) of TOR1.
  • Conditional depletion of TOR1 and TOR2 expression.
  • Utilizing TORC2-specific tor2-tsA and TORC1/TORC2-specific tor2-tsC conditional mutants.
  • Assessing pre-initiation complex (PIC) formation and transcription of ribosomal protein genes.

Main Results:

  • Null mutation or depletion of TOR1 does not affect PIC formation or transcription of ribosomal protein genes.
  • TORC2 is dispensable for ribosomal protein gene expression, as demonstrated by tor2-tsA mutants and TOR2 depletion.
  • Combined genetic inactivation of TOR1 and TOR2 (via tor1 null and tor2-tsC mutation) impairs PIC formation and reduces ribosomal protein gene transcription.
  • Tor1 and Tor2 exhibit redundant roles in PIC formation and transcription via TORC1.

Conclusions:

  • TORC2 is not required for ribosomal protein gene expression.
  • Tor1 and Tor2 function redundantly through TORC1 to regulate PIC formation and transcription of ribosomal protein genes.
  • Distinct genetic roles of Tor1 and Tor2 in ribosomal protein gene expression are mediated by TORC1.
Keywords:
RNA polymerase IITBPTORpre-initiation complexribosomal protein genes

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