Kathleen CollinsProfessor of Biochemistry and Molecular Biology*And Affiliate, Division of Cell and Developmental Biology E-mail: kcollins@socrates.berkeley.edu |
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Full Directory InformationResearch Interests
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The laboratory studies ribonucleoproteins (RNPs), with particular focus on the reverse transcriptase telomerase. Telomerase adds one strand of telomeric DNA simple sequence repeats to chromosome ends by copying a template within its integral RNA component. This de novo telomeric repeat addition is required to balance the loss of repeats that occurs with incomplete replication of linear chromosome ends by conventional DNA-dependent DNA polymerases. Cells that do not produce active telomerase, including most cells in multicellular organisms, lose telomeric repeats with each round of cell division. When telomeric repeat number reaches a critical minimum, short telomeres somehow signal for cell death or an irreversible proliferative senescence. Cancer cells escape this limitation by activating telomerase. We study telomerase both in vitro, to understand the structure and biochemical mechanisms of this novel reverse transcriptase, and in vivo, to define its cellular roles and regulations. We are also investigating structure and function in other RNPs with cellular activities that, like telomerase, may depend intimately on both protein and non-coding (nc) RNA.
Current Projects
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We are investigating telomerase in the ciliate Tetrahymena and human cells using techniques from structural biology and enzymology to cell biology and genetics. Some of these studies focus on the protein-nucleic acid interactions that establish the unique features of the telomerase enzyme. For example, the telomerase RNP must distinguish a short sequence within the much larger telomerase RNA as the template for reverse transcription. Also, as substrates for elongation, telomerase must be recruited to authentic chromosome ends but not random DNA breaks. Both of these specificities can be partially recapitulated with recombinant enzyme and are likely to be enhanced by as yet uncharacterized factors as well. We are using recombinant telomerase proteins and RNAs to study the roles of known molecules. We are using affinity purification techniques to identify new telomerase components and regulatory factors.
Although much is known about protein folding and RNA folding independently, the principles governing co-folding of protein and RNA in vivo remain unknown. Therefore, we are investigating cellular RNP biogenesis pathways. Our search for proteins involved in telomerase RNA processing and RNP assembly led us to discover that in human cells, telomerase shares a set of four proteins with another RNP family. One of these proteins was initially identified as the gene product of the locus mutant in X-linked dyskeratosis congenita (DC). We have shown that telomerase deficiency can completely account for the phenotypes of this human disease. We are now studying how telomerase is affected by DC gene mutations and how telomerase in normal and DC cells is regulated during cellular differentiation and oncogenesis.
The diversity of functional, non-protein coding RNA (ncRNA) is underestimated in most eukaryotes, due to difficult gene prediction, cloning and purification. Using methods developed in our studies of telomerase RNA and newly developed methods as well, we are identifying and characterizing functional RNAs in their cellular RNP context. We hope to understand the range of functions adopted by RNA in the diversification of proteins by their evolution to RNP.
Selected Publications
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Holoenzyme proteins required for the physiological assembly and activity of telomerase. [K.L. Witkin and K. Collins (2004) Genes Dev. 18, 1107-1118]
Distinct biogenesis pathways for human telomerase RNA and H/ACA small nucleolar RNAs. [D. Fu and K. Collins (2003) Mol. Cell 11, 1361-1372]
Roles for RNA in telomerase nucleotide and repeat addition processivity. [C.K. Lai, M.C. Miller and K. Collins (2003) Mol. Cell 11, 1673-1683]
Human telomerase reverse transcriptase motifs required for elongation of a telomeric substrate. [S.R. Lee, J.M. Wong and K. Collins (2003) J. Biol. Chem. 278, 52531-52536]
Subnuclear shuttling of human telomerase induced by transformation and DNA damage. [J.M. Wong, L. Kusdra and K. Collins (2002) Nature Cell Biol. 4, 731-736]
Telomerase recognizes its template using an adjacent RNA motif. [M.C. Miller and K. Collins (2002) Proc. Natl. Acad. Sci. USA, 99, 6585-6590]
Template boundary definition in Tetrahymena telomerase. [C.K. Lai, M.C. Miller and K. Collins (2002) Genes Dev. 16, 415-420]
Telomerase in the human organism. [K. Collins and J.R. Mitchell (2002) Oncogene 21, 564-579]
The RNA binding domain of telomerase reverse transcriptase. [C.K. Lai, J.R. Mitchell and K. Collins (2001) Mol. Cell. Biol. 21, 990-1000]
Requirements for the dGTP-dependent repeat addition processivity of recombinant Tetrahymena telomerase. [C.D. Hardy, C.S. Schultz and K. Collins (2001) J. Biol. Chem. 276, 4863-4871]
Template definition by Tetrahymena telomerase reverse transcriptase. [M.C. Miller, J.K. Liu and K. Collins (2000) EMBO J. 19, 4412-4422]
Human telomerase activation requires two independent interactions between telomerase RNA and telomerase reverse transcriptase. [J.R. Mitchell and K. Collins (2000) Mol. Cell (2000) 6, 361-371]
A novel telomerase component defective in the human disease dyskeratosis congenita. [J.R. Mitchell, E. Wood and K. Collins (1999) Nature 402, 551-555]
