UC Santa Cruz

Eukaryotic organisms contain linear chromosomes that are protected by telomeres; long repeated sequences that act as a protecting buffer from the shortening of chromosomes during each replication cycle, and as a signal that identify the ends from double stranded breaks. Telomeres are maintained in most organisms by a ribonucleoprotein called telomerase. While telomeres and telomerase have been implicated in many human diseases, including cancer, very little is known about the unique enzymatic mechanism of telomerase, making it difficult to develop medicinal therapeutics.

The protein p65 is required for telomerase assembly in Tetrahymena thermophila. Using RNase footprinting and single molecule FRET, we show that the C-domain of p65 is not only required, but is sufficient for telomerase assembly, paving the way for understanding possible p65 homologues in other organisms. Preliminary crystals of complexes consisting of the RNA binding domain of the catalytic subunit and the RNA component of T. thermophila were also obtained. Because the catalytic subunit is quite conserved between species, any structure obtained from these crystals will prove valuable in understanding the RNA and protein organization of telomerase.

For a more ambitious goal, a novel method was pursued to solve the structure of telomerase: inserting telomerase RNA into ribosomal RNA, assembling the telomerase complex on the ribosome, using the well known ribosome purification methods and crystallization conditions, and thus using the ribosome as a crystallization chaperone and scaffold. While crystals failed to diffract to a desired resolution, considerable strides were made toward this method that could also be extended to other ribonucleoproteins.