Three telomerases with completely non-telomeric template replacements are catalytically active

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Telomerase, a reverse transcriptase, is crucial for maintaining telomere length.
• Its activity relies on a protein subunit and an RNA component with a templating region.
• Mutations in the RNA template can impair telomerase function.

Purpose of the Study:

• To investigate the functional necessity of the native telomerase RNA templating region.
• To determine if non-telomeric sequences can replace the native template in vivo.
• To explore the role of base-specific interactions in telomerase activity.

Main Methods:

• Complete replacement of the *TETRAHYMENA thermophila* telomerase templating region with non-telomeric sequences in vivo.
• In vitro enzymatic assays to assess polymerization activity and processivity.
• In vivo studies to evaluate telomere length changes.
• Analysis of primer recognition and DNA cleavage reactions.

Main Results:

• Modified telomerases (U9, AUN, AU4) retained in vitro polymerization activity.
• In vivo, AUN and AU4 telomerases induced telomere shortening.
• Demonstrated in vitro fidelity of AUN and U9 telomerases.
• Showed 5' end primer recognition is independent of template base pairing.
• Observed abnormal DNA cleavage with the AUN template.

Conclusions:

• Base-specific interactions between the telomerase template and protein are not essential for core telomerase functions.
• Nucleotide addition and base discrimination can occur with substituted templates.
• This challenges the absolute requirement for native template sequences in telomere maintenance.