Tetrahymena telomerase ribonucleoprotein RNA-protein interactions

Telomerase is an enzyme that is essential for the replication and maintenance of chromosomal termini, It is a ribonucleoprotein consisting of a catalytic subunit, one or more associated proteins, and an integral RNA subunit that serves as a template for the synthesis of telomeric repeats. We identified a Tetrahymena telomerase RNA-protein complex by an electrophoretic mobility shift assay, using telomerase partially purified from whole cell extracts and radiolabeled, in vitro transcribed wild-type Tetrahymena telomerase RNA. Complex formation was specific as unlabeled Tetrahymena telomerase RNA, but not Escherichia coli ribosomal RNAs, competitively inhibited complex formation. Binding required concentrations of MgCl2 of at least 10 mM and occurred over a wide range of potassium glutamate concentrations (20-220 mM), The RNA-protein complex was optimally reconstituted with a 30 degrees C preincubation for less than or equal to 5 min, prior to electrophoresis. Certain Tetrahymena telomerase RNAs containing deletions of structures and sequences previously predicted to be involved in protein binding were unable to competitively and specifically inhibit complex formation, suggesting a role in protein binding for the deleted residues or structures.