A novel motif in telomerase reverse transcriptase regulates telomere repeat addition rate and processivity

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• Telomerase is a reverse transcriptase enzyme responsible for maintaining telomere length by adding DNA repeats to chromosome ends.
• Telomere maintenance is crucial for cellular stability and preventing premature aging.
• The catalytic domain of telomerase reverse transcriptase (TERT) contains conserved regions essential for its enzymatic activity.

Purpose of the Study:

• To characterize a novel, evolutionarily conserved telomerase-specific motif, termed motif 3, within the TERT catalytic domain.
• To investigate the role of motif 3 in regulating telomerase activity, specifically the rate and processivity of telomere repeat addition.
• To elucidate the mechanism by which motif 3 influences template translocation and DNA-RNA realignment during telomere synthesis.

Main Methods:

• Comprehensive site-directed mutagenesis of motif 3 in telomerase reverse transcriptase.
• In vitro reconstitution and biochemical assays of mutant telomerase enzymes.
• Functional analysis of mutant telomerases in cellular contexts.
• Assessment of telomere repeat addition rate, processivity, and primer utilization.

Main Results:

• Mutations in motif 3 independently modulated the rate and processivity of telomere repeat addition.
• Hyperactive mutants displayed increased repeat addition rates and faster enzyme turnover, indicative of enhanced strand-separation during template translocation.
• Processivity of motif 3 mutants correlated strongly with their ability to utilize an 8-nucleotide DNA primer, suggesting motif 3's role in DNA-RNA realignment.
• Motif 3 is conserved across vertebrates and ciliates, highlighting its fundamental importance.

Conclusions:

• Motif 3 is a critical determinant of both telomerase activity and processivity.
• The findings provide mechanistic insights into template translocation and DNA-RNA realignment during telomere synthesis.
• Motif 3 represents a key regulatory element in the telomere maintenance machinery.