Lockhart, PJ, Larkum, AW, Steel, M, Waddell, PJ & Penny, D 1996, 'Evolution of chlorophyll and bacteriochlorophyll: the problem of invariant sites in sequence analysis.', Proceedings of the National Academy of Sciences, vol. 93, no. 5, pp. 1930-1934.
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Competing hypotheses seek to explain the evolution of oxygenic and anoxygenic processes of photosynthesis. Since chlorophyll is less reduced and precedes bacteriochlorophyll on the modern biosynthetic pathway, it has been proposed that chlorophyll preceded bacteriochlorophyll in its evolution. However, recent analyses of nucleotide sequences that encode chlorophyll and bacteriochlorophyll biosynthetic enzymes appear to provide support for an alternative hypothesis. This is that the evolution of bacteriochlorophyll occurred earlier than the evolution of chlorophyll. Here we demonstrate that the presence of invariant sites in sequence datasets leads to inconsistency in tree building (including maximum-likelihood methods). Homologous sequences with different biological functions often share invariant sites at the same nucleotide positions. However, different constraints can also result in additional invariant sites unique to the genes, which have specific and different biological functions. Consequently, the distribution of these sites can be uneven between the different types of homologous genes. The presence of invariant sites, shared by related biosynthetic genes as well as those unique to only some of these genes, has misled the recent evolutionary analysis of oxygenic and anoxygenic photosynthetic pigments. We evaluate an alternative scheme for the evolution of chlorophyll and bacteriochlorophyll.
Roche, JL, van der Staay, GWM, Partensky, F, Ducret, A, Aebersold, R, Li, R, Golden, SS, Hiller, RG, Wrench, PM, Larkum, AWD & Green, BR 1996, 'Independent evolution of the prochlorophyte and green plant chlorophyll a/b light-harvesting proteins', Proceedings of the National Academy of Sciences, vol. 93, no. 26, pp. 15244-15248.
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The prochlorophytes are oxygenic prokaryotes differing from other cyanobacteria by the presence of a light-harvesting system containing both chlorophylls (Chls) a and b and by the absence of phycobilins. We demonstrate here that the Chl a/b binding proteins from all three known prochlorophyte genera are closely related to IsiA, a cyanobacterial Chl a -binding protein induced by iron starvation, and to CP43, a constitutively expressed Chl a antenna protein of photosystem II. The prochlorophyte Chl a/b protein ( pcb ) genes do not belong to the extended gene family encoding eukaryotic Chl a/b and Chl a/c light-harvesting proteins. Although higher plants and prochlorophytes share common pigment complements, their light-harvesting systems have evolved independently.
STEPHENSON, KA, LEAN, IJ & O'MEARA, TJ 1996, 'The effect of monensin on the chemotactic function of bovine neutrophils', Australian Veterinary Journal, vol. 74, no. 4, pp. 315-317.
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