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- Söderbom, Fredrik
(author)
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Structure, function and metabolic stability of antisense RNAs
- 1997
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Doctoral thesis (other academic/artistic)abstract
- Antisense RNAs usually are small, highly structured, unstable RNAs that control a varietyof different biological processes. They exert their effect by binding to complementarytarget RNAs and thereby inhibit their functions.This thesis is concerned with the main features that determine the efficiency of antisense RNAs: their metabolic stability, the binding rate between antisense and target RNA, and the structure of the antisense RNA itself. Three different plasmid-encoded antisense RNAs were studied.RNA decay in bacteria is complex: a large number of proteins are involved in processing and degradation. My results show that mutations in an Escherichia coli gene, pcnB, encoding a poly(A)polymerase, exert an effect on the replication of antisense RNA-regulated plasmids. PcnB aids in the degradation of the inhibitors of replication, the antisense RNAs. This enzyme can polyadenylate both CopA and RNAI, the antisense RNAs controlling the replication of plasmids R1 and ColE1, respectively. Accelerated pcnB dependent decay of CopA requires processing by an endoribonuclease, RNase E. This cleavage step appears to initiate decay of both CopA and RNA I. In addition, the 3'-5' exoribonucleases PNPase and RNase II can independently degrade RNase E-cleaved CopA.Other ribonucleases are involved in the pcnB dependent degradation since CopA decay is shown (although at lower rates) in the absence of these enzymes.Analysis of FinP, an antisense RNA controlling plasmid conjugation, indicates astructure consisting of two stem-loops. Stem-loops are preferred motifs in most antisenseRNAs. The binding rate between FinP and its target RNA is in the same range as in otherwell-characterized systems. Upon binding, the target RNA (traJ mRNA) is renderedunstable, probably due to RNase III-dependent cleavages. This destabilization requiresthe presence of the helper protein FinO.
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- Fredriksson, Charlotta, 1968-
(author)
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Nitrogenase localisation reveals cell differentiation in filamentous, non-heterocystous cyanobacteria
- 1996
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Doctoral thesis (other academic/artistic)abstract
- This thesis deals with detecting and interpreting natural and anthropogenic changes in the composition of the Arctic troposphere. It also covers quantifications of regional climate change due to the activities of mankind. By comparing observed temperature trends and calculated sulfate burdens over the globe, it was found that the two regions affected by a substantial increase in atmospheric loading of anthropogenic sulfate - Europe and China - displayed a decrease in summer temperatures between the 1940s and the 1980s. The cooling is consistent with recent studies indicating a negative radiative forcing by anthropogenic sulfate particles. The second part of the thesis concentrates on the interpretation of day-to-day variations in atmospheric carbon dioxide (CO2) mixing ratio measured at a monitoring station on Spitsbergen. Studies using three-dimensional back trajectories covering several spring-periods show that recent oceanic CO2 uptake was discernable in the Spitsbergen data. These findings were supported by complementary calculations from a simple Lagrangian model, using realistic CO2-saturations in the northern North Atlantic. In order to further interpret these and similar short-term variations in the atmospheric composition on Spitsbergen, a high-resolution regional transport model was developed. This model is driven by observed meteorology, with a parameterised boundary layer, and utilizes a mass conserving advection scheme with only small phase and amplitude errors. Tests showed that the model was able to simulate realistic seasonal and spatial variations of radon-222 in the lower troposphere. The model was next applied to a spring period in the Arctic. By comparing calculated CO2 mixing ratios with measurements taken on Spitsbergen it was possible to discriminate between oceanic and terrestrial CO2 uptake. These findings are encouraging for the further use of this model in detecting and quantifying CO2 fluxes in the high latitude northern hemisphere. In a final study the transport model was used to compare different estimates of fossil fuel CO2 emissions in Eurasia. The calculations showed that the Arctic troposphere is efficiently ventilated in winter, with an e-folding time on the order of 10 days. It was also shown that anthropogenic CO2 emissions in Siberia can not be distributed in proportion to population density, which has previously been done. There is, strong evidence of large combustion sources near the gas-fields around the Gulf of Ob, and in the interior of Eastern Siberia. The model results suggest that these emission regions are a dominating source for the formation of Arctic haze in winter.
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