| Photosynthesis is arguably the most important biological process on earth. The photosynthetic bacteria is a kind of anaerobic photosynthetic prokaryotes being found everywhere.Photosynthesis is the single most important process developed by nature, providing all of the biological energy needed for higher forms of life to exist. Bacterial photosynthetic membranes contain thousands of pigment molecules (bacteriochlorophylls and carotenoids) that are non-covalently bound to proteins to form well organized pigment-protein complexes.The basic mechanisms of photosynthetic light-harvesting and reaction center (RC) photochemistry which has been researched on understanding of the reactions taking place in the early events of photosynthesis is in its membrane.The photosynthetic apparatus of purple bacteria is a nanometric assembly in the intracytoplasmic membranes and consists of pigment-protein complexes, the photosynthetic RC (Reaction Center) and LH(Light Harvesting). The primary processes of photosynthesis involve absorption of photons by light-harvesting complexes (LH), transfer of excitation energy from LH to the photosynthetic reaction centers (RC), and the primary charge separation across the photosynthetic membrane.Many species of purple nonsulfur photosynthetic bacteria regulate the synthesis of their photosynthetic apparatus in response to alterations in oxygen tension and light intensity.Responding to low oxygen tensions and light intensity, the purple nonsulfur bacterium is capable of developing a series of intracytoplasmic invaginations of the cell membrane, which house the photosynthetic apparatus. The photosynthetic apparatus contains three major carotenoid-bacteriochlorophyll (Bchl)-protein complexes, B800-850 (LHII) and B875 (LHI), which are light-harvesting complexes, and the reaction center (RC) complex.The pigment protein complexes which carry out light harvesting and primary photochemistry are localized in the intracytoplasmic membrane. Energy is transfered from LHII to RC via LHI or directly to the RC, where the primary energy conversion takes place. The light harvesting complex (LHI) absorbs maximally in the near-infrared at approximately 875 nm(LHI). LHI receives energy from the peripheral light harvesting complex(LHII), which has absorption bands at 800 and 850 nm. Both types of LH complexes are composed of two membranespanning polypeptides,αandβ, that anchor bacteriochlorophyll and carotenoids in the membrane.Previously, in a study of regulation of the pucBAC operon of R. sphaeroides, it was observed that following deletion of the puc1BA genes there was a highly homologous second transcript that was approximately to 1.3 kb long, judged by hybridization. But it is unknown about its expression and function.Molecular biology techniques and spectroscopic analysis were applied to research the expression and function of puc2BA. puc2BA was amplified by polymerase chain reaction, and cloned acrossly with puc1BA into pRK415 vector controlled by puc promoter from R. sphaeroides, which was then introduced into LHI and LHII-minus R. sphaeroides mutants. Then the transconjugant strains were analysedRdv.sulfidophilum and R. sphaeroides belong to different generas of photosynthetic bacteria. pucsBA was amplified by polymerase chain reaction, and cloned into pRK415 vector controlled by puc promoter from R. sphaeroides, which was then introduced into LHI and LHII-minus R. sphaeroides mutants; the expression and function of transconjugant strains were examined.Some conclusions as below were draw from the results of these experiments.1. The puc2BA gene of R. sphaeroides was normally expressed and functional, but there have to be the product of pucC in R. sphaeroides at the same time.2. The amount of assembled LHII of puc2BA in R. sphaeroides is much lowler than which of puc1BA, the former is much lower to about 19.60% of the latter. The semiquantitative RT-PCR revealed that the mRNA levels of puc2B, puc2A were lower than those of puc1B, puc1A in R. sphaeroides, and there was no apparent difference in mRNA levels between puc1BA and puc2BA transcribed from the expression vectors, but the amounts of LHII complex from puc2BA were not increased correspondingly to the levels matched to the LHII complex from puc1BA in R. sphaeroides. The puc2BA- encoded polypeptides assembling LHII complex is not efficiently as do puc1BA- encoded polypeptides, the puc2AB-encoded polypeptides are merely supplement for the LHII complex of R. sphaeroides.3. After puc2BA was matched acrossly with puc1BA, and introduced into DD13, the transconjugant strains had the ability to assemble LHII.4. The pucsBA gene of Rdv. sulfidophilum was normally expressed and functional, the Rdv. sulfidophilum LHII has its character in DD13. The absorbance spectra and Bchl concentration of the membrane samples clearly showed that the assembly and spectral properties of the Rdv. sulfidophilum LHII complex are lower to 70.13% of which of R. sphaeroides.5. The pucsBA gene of Rdv. sulfidophilum and the pufBA gene of R. sphaeroides were cloned in the expressed vector and introduced in DD13, the heterologous LHII and native LHI were produced and assembled in the membrane.The results were helpful to analyze the function and expression character of homologous genes in genome and the regulation mechanism through the evolvement course, and the relationship between structure and function of genome.Rdv. sulfidophilum pucsBA was expressed and assembled LHII in R. sphaeroides. we can deduce that the evolvement relationship between Rdv. sulfidophilum and R. sphaeroides and the possible crystal structure of Rdv. sulfidophilum.It is also helpful to understand what the molecule mechanism photosynthetic bacteria capture sun energy. Heterologous genes of functional membrane protein was normally expressed, which provides some method to produced heterologous functional membrane protein in this system.
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