Ultra-violet mutagenesis of Synechocystis sp. 6701: mutations in chromatic adaptation and phycobilisome assembly

Mutations affecting pigmentation of the cyanobacterium Synechocystis sp. 6701 were induced with ultraviolet light. Two mutants with phycobilisome structural changes were selected for structural studies. One mutant, UV08, was defective in chromatic adaptation and incorporated phycoerythrin into phycobilisomes in white or red light at a level typical of growth in green light. The other mutant, UV16, was defective in phycobilisome assembly: little phycocyanin was made and none was attached to the phycobilisome cores. The cores were completely free of any rod substructures and contained the major core peptides plus the 27,000 M_r linker peptide that attaches rods to the core. Micrographs of the core particles established their structural details. Phycoerythrin in UV 16 was assembled into rod structures that were not associated with core material or phycocyanin. The 30,500 M_r and 31,500 M_r linker peptides were present in the phycoerythrin rods with the 30,500 M_r protein as the major component. Phycobilisome assembly in vivo is discussed in light of this unusual mutant.Abbreviations PE phycoerythrin - PC phycocyanin - AP allophycocyanin - W white light - G green light - R red light - SDS sodium dodecyl sulfate - Na–K–PO₄ equimolar solutions of NaH₂PO₄ · H₂O and K₂HPO₄ · 3 H₂O titrated to the desired pH     

A Suggested Pioneer Organism for the Wächtershäuser Origin of Life Hypothesis

A suggested pioneer organism for the Wächtershäuser origin of life hypothesis is presented. In this scenario, a cubic pyrite crystal edge serves as a catalytic surface for the production of a proto-nucleic acid. Computational analysis demonstrates how the vacant cubic pyrite edge could be populated by iron(II) and hydrogen phosphate, capped with a distorted iron pentacarbonyl. A bridging iron sulfide then forms blocking one side of the edge. The carbonyl on the other side of the edge can then react with either existing uracil or cytosine, to produce a nitrogen-iron carbonyl intermediate. This intermediate serves as a free radical initiator for a polymerization of carbon monoxide and molecular hydrogen. After the fourth carbon is added to the chain, the polymerization is terminated by ring formation yielding a condensed ribose. The resultant product is a proto-nucleic acid, a pioneer organism.