The role of membrane-bound transcriptional and translational machineries in the biogenesis of photosynthetic membranes of the cyanobacterium Phormidium laminosum

摘要

A fraction of membranes, the predominant component of which had electron-microscopic image resembling that of primary membranes from pea etiochloroplasts, was isolated from the cyanobacterium Phormidium laminosum. These electron-transparent membranes contained electron-dense inclusions, which were similar to those found earlier in primary membranes of pea etiochloroplasts. These inclusions were identified as structures characteristic of the four early stages of primary membrane biogenesis in etiochloroplasts: (1) primary transcript synthesis, (2) transcript processing (splicing), (3) ribosome formation, and (4) polyribosomes assemblage. However, in spite of the similarity in the shape and size of polyribosomes produced in membranes, the later stages of membrane biogenesis differed in pea etiochloroplasts and in the cyanobacterium. Instead of fretlike structures of etiochloroplasts, thickenings of which produce prothylakoids and, later, granal thylakoids, the final stage of the photosynthetic membrane biogenesis in the cyanobacterium resulted in the formation of rodlike structures. The conclusion is that molecular mechanisms of early biogenesis of photosynthetic membranes are common in chloroplasts and cyanobacteria; a specificity of final stages is discussed.