Rapid evolutionary divergence of Photosystem I core subunits PsaA ...

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134 Figure 1. Alignment of the PsaA (A) and PsaB (B) from the marine prokaryotes Prochlorococcus sp. MED4, Prochlorococcus marinus SS120 and Synechococcus WH7803. For comparison, the corresponding sequences of the freshwater cyanobacterium Synechocystis PCC6803 is included. The putative membrane spanning helices I–XI and the extramembrane loops A–L, determined and numbered based on the analogy to the model presented by Sun et al. (1997) are indicated. The cysteines that ligate the F x electron acceptor are indicated with a block. For positions where amino acids were identical, only the amino acid for Prochlorococcus sp. MED4 is given. Gaps are indicated by -. 731–743 amino acids reported for most other organisms. Most diverse is loop E between the helices IV and V and loop H between helices VII and VIII, the areas that are the least conserved in all PsaB pro-
135 Figure 1. Continued. teins. The C-terminal domains of PsaA and PsaB, from helices VIII to XI, that are thought to bind the components of the electron transport chain including the F x -binding domain, are the most conserved regions. In all phylogenetic analyses using the concatenated PsaA and PsaB sequences, the Prochlorococcus strains grouped together with the marine Synechococcus strain (Figure 2), separately from the other cyanobacteria. Analyses of either PsaA or PsaB lead to comparable results. Inclusion of the sequences from the dinoflagellate Heterocapsa triquetra resulted in a destabilization of the trees, due to the high divergence of these sequences. Depending on small differences in the alignments and the inclusion or omission of gaps, Heterocapsa grouped together with Guillardia and Odontella or with the Prochlorococcus/Synechococcus cluster (not shown).
Page 1 and 2: Photosynthesis Research 65: 131-139
Page 3: 133 X63768, Synechococcus PCC7002:
Page 7 and 8: 137 Table 1. Sequence identity of P
Page 9: 139 Garczarek L, Hess W, Holtzendor

Rapid evolutionary divergence of Photosystem I core subunits PsaA ...

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