abstract: Telomerase is a specialized enzyme that adds telomeric DNA repeats to the chromosome ends to counterbalance the progressive telomere shortening over cell divisions. It has two essential core components, a catalytic telomerase reverse transcriptase protein (TERT), and a telomerase RNA (TR). TERT synthesizes telomeric DNA by reverse transcribing a short template sequence in TR. Unlike TERT, TR is extremely divergent in size, sequence and structure and has only been identified in three evolutionarily distant groups. The lack of knowledge on TR from important model organisms has been a roadblock for vigorous studies on telomerase regulation. To address this issue, a novel in vitro system combining deep-sequencing and bioinformatics search was developed to discover TR from new phylogenetic groups. The system has been validated by the successful identification of TR from echinoderm purple sea urchin Strongylocentrotus purpuratus. The sea urchin TR (spTR) is the first invertebrate TR that has been identified and can serve as a model for understanding how the vertebrate TR evolved with vertebrate-specific traits. By using phylogenetic comparative analysis, the secondary structure of spTR was determined. The spTR secondary structure reveals unique sea urchin specific structure elements as well as homologous structural features shared by TR from other organisms. This study enhanced the understanding of telomerase mechanism and the evolution of telomerase RNP. The system that was used to identity telomerase RNA can be employed for the discovery of other TR as well as the discovery of novel RNA from other RNP complex. / Dissertation/Thesis / Ph.D. Biochemistry 2011

Determining the cosmic star formation history of the Universe is fundamental for our understanding of galaxy formation and evolution. While surveys now suggest that the "epoch" of galaxy formation occurred more than 6 billion years ago, our measurements still suff er from signi ficant scatter and uncertainties due to the use of diff erent indicators, dust extinction and the e ffects of cosmic variance in the current samples. Furthermore, understanding galaxy formation and evolution require us to go much beyond simply determining the star formation history of the Universe with high accuracy: what are the physical mechanisms driving the strong evolution that we observe? How does star formation depend on stellar mass and environment and how does that change with cosmic time? This thesis presents both a completely self-consistent determination of the star formation history of the Universe (based on a single, sensitive and well-calibrated star formation indicator up to redshift z ~ 2:3: the H α luminosity) and investigates its drivers by exploring large area surveys (probing a range of environments and overcoming cosmic variance) obtained with the High-redshift Emission Line Survey (HiZELS). HiZELS is a panoramic extragalactic survey using the WFCAM instrument on the 3.8-m UK Infrared Telescope (UKIRT) which utilizes a set of existing and custom-made narrow-band filters in the J, H and K bands to detect emission line galaxies (main targets are H α emitters at z = 0:84, z = 1:47 and z = 2:23) up to z ~ 9 over square degree areas of extragalactic sky. Detailed measurements of the H α luminosity function and its evolution with redshift are presented, revealing a signi ficant luminosity evolution. The clustering properties of H α emitters at high-redshift are quantifi ed and investigated for the first time, revealing that these distant galaxies reside in Milky-Way type dark matter haloes at z ~ 1. Mass and environment are found to have important and inter-dependent roles on star formation at high-z and the results are able to reconcile previously contradictory results in the literature. Furthermore, by conducting a novel double-narrow band survey at z = 1:47, the relationship between the [Oii]3727 and H α emission lines is studied in detail and directly compared to z ~ 0, showing no signifi cant evolution in the dust properties of star-forming galaxies, despite the very strong luminosity evolution. Finally, this thesis also presents the widest search for very distant Ly α emitters at z ~ 9.

Theories of how galaxies form and evolve depend greatly on constraints provided by observations. However, when those observations come from different datasets, systematic offsets may occur. This causes difficulties measuring variations in parameters between filters. In this thesis I present the variation in total luminosity density with wavelength in the nearby Universe (z<0.1), produced from a consistent reanalysis of NIR and optical observations, taken from the MGC, UKIDSS and SDSS surveys. I derive luminosity distributions, best-fitting Schechter function parameterisations and total luminosity densities in ugrizYJHK, and compare the variation in luminosity density with cosmic star formation history (CSFH) and initial mass function (IMF) models. I examine the r band luminosity distribution produced using different aperture definitions, the joint luminosity- surface brightness (bivariate brightness) distribution in ugrizYJHK, comparing them to previously derived distributions, and how the total luminosity density varies with wavelength when surface brightness incompleteness is accounted for. I find the following results. (1) The total luminosity density calculated using a non-Sersic (e.g. Kron or Petrosian) aperture is underestimated by at least 15%, (2) Changing the detection threshold has a minor effect on the best-fitting Schecter parameters, but the choice of Kron or Petrosian apertures causes an offset between datasets, regardless of the filter used to define the source list, (3) The decision to use circular or elliptical apertures causes an offset in M* of 0.20 mag, and best-fitting Schechter parameters from total magnitude photometric systems have a flatter faint-end slope than Kron or Petrosian photometry, (4) There is no surface brightness distribution evolution with luminosity for luminous galaxies, but at fainter magnitudes the distribution broadens and the peak surface brightness dims. A Choloniewski function that is modified to account for this surface brightness evolution fits the bivariate-brightness distribution better than an unmodified Choloniewski function, (5) The energy density per unit interval, vf(v) derived using MGC and GAMA samples agrees within 90% confidence intervals, but does not agree with predictions using standard CSFH and IMF models. Possible improvements to the data and alterations to the theory are suggested.