The light-harvesting complexes (LHCs) are a superfamily of chlorophyll-binding proteins present in all photosynthetic eukaryotes. The Lhc genes are nuclear-encoded, yet the pigment-protein complexes are localized to the thylakoid membrane and provide a marker to follow the evolutionary paths of plastids with different pigmentation. The LHCs are divided into the chlorophyll a/b-binding proteins of the green algae, euglenoids, and higher plants and the chlorophyll a/c-binding proteins of various algal taxa. This work examines the phylogenetic position of the LHCs from three additional taxa: the rhodophytes, the cryptophytes, and the chlorarachniophytes. Phylogenetic analysis of the LHC sequences provides strong statistical support for the clustering of the rhodophyte and cryptomonad LHC sequences within the chlorophyll a/c-binding protein lineage, which includes the fucoxanthin-chlorophyll proteins (FCP) of the heterokonts and the intrinsic peridinin-chlorophyll proteins (iPCP) of the dinoflagellates. These associations suggest that plastids from the heterokonts, haptophytes, cryptomonads, and the dinoflagellate, Amphidinium, evolved from a red algal-like ancestor. The Chlorarachnion LHC is part of the chlorophyll a/b-binding protein assemblage, consistent with pigmentation, providing further evidence that its plastid evolved from a green algal secondary endosymbiosis. The Chlorarachnion LHC sequences cluster with the green algal LHCs that are predominantly associated with photosystem II (LHCII). This suggests that the green algal endosymbiont that evolved into the Chlorarachnion plastid was acquired following the emergence of distinct LHCI and LHCII complexes.

Two distinct cDNAs encoding putative factors of plastid RNA polymerase were isolated from Zea mays, a C4 plant. The deduced amino acid sequences of both cDNAs possess all four highly conserved domains proposed for recognition of ؊10 and ؊35 promoter elements, core complex binding, DNA binding, and melting. These two cDNAs are designated sig1 and sig2. Phylogenetic analysis of available plastid factors indicated that they were probably the descendants of cyanobacterial principal factors. Southern blots probed with sig1 and sig2 revealed that both genes exist in the maize nuclear genome as single-copy genes, but lowstringency hybridization suggested the presence of a multigene family of maize plastid factors. Transcription of sig1 and sig2 is light inducible and tissue specific. Transcripts of sig1 and sig2 were abundant in greening leaf tissues; sig2 (but not sig1) was barely detectable in etiolated leaves and neither was detectable in roots. Immunological studies using a peptide antibody against an epitope in subdomain 2.4 of Sig1 revealed 50-kDa and 60-kDa immunoreactive proteins in maize chloroplasts. Reduced levels of the 60-kDa immunoreactive protein were detected in etioplasts, and no immunoreactive proteins were observed in roots. Collectively, the data suggest that the nuclear genes, sig1 and sig2, may play a role in differential expression of plastid genes during chloroplast biogenesis.Plastids of algae and higher plants are semiautonomous organelles that possess their own genetic information. Plastids contain circular, double-stranded DNA genomes that encode up to 120 genes for transcription, translation, and photosynthesis (1). Transcription of plastid genes depends on plastidspecific, DNA-dependent RNA polymerases (RNAPs). Two independent plastid RNAPs have been characterized, the bacterial-type multisubunit RNAP (2) and the bacteriophagetype single subunit RNAP (3-5). The holoenzyme of bacterial RNAP consists of a core complex (␣ 2 ␤␤Ј) and a factor. The subunit confers the holoenzyme with the ability to recognize Ϫ35 and Ϫ10 promoter motifs, leading to accurate initiation of transcription (6).The functional enzymes of bacterial-type RNAP have been isolated from plants, and genes encoding the core subunits have been identified in plastid genomes (2). However, complete sequences of the plastid genomes of several species did not reveal any ORF homologous to factors. Because Ϫ35 and Ϫ10 elements exist widely in plastid gene promoters, and immunological evidence indicates that chloroplast RNAPs contain polypeptides that crossreact with antibodies against a principal cyanobacterial factor, it seems likely that RNAP factors are encoded in the nuclear genomes of plants (7).Recently, nuclear genes encoding factors of plastid RNAP have been isolated from red algae (8, 9) and higher plants (10-12).Induction of plastid gene transcription by a light signal is a complex process, probably involving numerous proteins in a cascade of reactions that are not well understood (13). Plastid factors may play a key...

Photosynthetic activity, chloroplast enzymes, and poly‐peptides were compared in green and red (ketocarotenoid‐containing) cultures of the microalga Haematococcus pluvialis Flotow. Green cultures, grown at 80 μmol pho‐tons.m‐2. s‐1 in an acetate‐containing medium, had a mean generation time of 27 h. Ketocarotenoid accumulation was induced by transfer of green cultures to PO4‐deficient medium and exposure to 250 μmol photons.m‐2. s‐1. Under these conditions, there was no increase in cell number, and the cultures turned red. Relative amounts of enzymes and thylakoid polypeptides in red and green cells were ascertained by immunoprobing with standardization on a chlorophyll (Chl) basis. In red cultures, the level of cytochrome f was greatly decreased (< 1% of green cell level), which is expected to greatly impair the linear electron flow from photosystem (PS) II to PS I. Also, the levels of apoproteins in red cells, namely, of CPI, D2, CP47, LHC I, and ribulose‐1, 5‐bisphosphate carboxylase were reduced to 15, 18, 29, 48, and 80%, respectively, of those in green cells. Only adenosine triphosphate syn‐thase exhibited no significant change in the two types of cultures. The respiration rate of red cultures was much higher (100 μmoles O2. mg Chl‐1.h‐1) than that of green cells (16 μmoles O2. mg Chl‐1.h‐1). Conversely, net O2 evolution (at Pmax in green cultures was 80 μmoles O2. mg Chl‐1.h‐1 but was —40 μmoles O2. mg Chl‐1.h‐1 in red cultures. PS II activity was demonstrated in broken cells of both green and red cultures, showing activity of 40 and 15 μmoles DCPIP‐mg Chl‐1.h‐1 (with DPC as electron donor), respectively. In contrast, PS I activity measured by the Mehler reaction showed that red rather than green cells had a greater activity (64 vs. 46 μmoles O2. mg Chl‐1.h‐1, respectively). Thus, in spite of the decline of O2 evolution in red cells, the photosystems were still functional. We postulate that the decline of O2, evolution in red cells is largely attributable to an increase in the respiration rate and the impairment of linear electron flow from PS II to PS I and, to some extent, to a decrease in components of the photosystems.

The oral streptococci are spherical Gram-positive bacteria categorized under the phylum Firmicutes which are among the most common causative agents of bacterial infective endocarditis (IE) and are also important agents in septicaemia in neutropenic patients. The Streptococcus mitis group is comprised of 13 species including some of the most common human oral colonizers such as S. mitis, S. oralis, S. sanguinis and S. gordonii as well as species such as S. tigurinus, S. oligofermentans and S. australis that have only recently been classified and are poorly understood at present. We present StreptoBase, which provides a specialized free resource focusing on the genomic analyses of oral species from the mitis group. It currently hosts 104 S. mitis group genomes including 27 novel mitis group strains that we sequenced using the high throughput Illumina HiSeq technology platform, and provides a comprehensive set of genome sequences for analyses, particularly comparative analyses and visualization of both cross-species and cross-strain characteristics of S. mitis group bacteria. StreptoBase incorporates sophisticated in-house designed bioinformatics web tools such as Pairwise Genome Comparison (PGC) tool and Pathogenomic Profiling Tool (PathoProT), which facilitate comparative pathogenomics analysis of Streptococcus strains. Examples are provided to demonstrate how StreptoBase can be employed to compare genome structure of different S. mitis group bacteria and putative virulence genes profile across multiple streptococcal strains. In conclusion, StreptoBase offers access to a range of streptococci genomic resources as well as analysis tools and will be an invaluable platform to accelerate research in streptococci. Database URL: http://streptococcus.um.edu.my.

The Porphyridium cruentum light harvesting complex (LHC) binds Chl a, zeaxanthin and beta-carotene and comprises at least 6 polypeptides of a multigene family. We describe the first in vitro reconstitution of a red algal light-harvesting protein (LHCaR1) with Chl a/carotenoid extracts from P. cruentum. The reconstituted pigment complex (rLHCaR1) is spectrally similar to the native LHC I, with an absorption maximum at 670 nm, a 77 K fluorescence emission peak at 677 nm (ex. 440 nm), and similar circular dichroism spectra. Molar ratios of 4.0 zeaxanthin, 0.3 beta-carotene and 8.2 Chl a per polypeptide for rLHCaR1 are similar to those of the native LHC I complex (3.1 zeaxanthin, 0.5 beta-carotene, 8.5 Chl a). The binding of 8 Chl a molecules per apoprotein is consistent with 8 putative Chl-binding sites in the predicted transmembrane helices of LHCaR1. Two of the putative Chl a binding sites (helix 2) in LHCaR1 were assigned to Chl b in Chl a/b-binding (CAB) LHC II [Kühlbrandt et al. (1994) Nature 367: 614-21]. This suggests either that discrimination for binding of Chl a or Chl b is not very specific at these sites or that specificity of binding sites evolved separately in CAB proteins. LHCaR1 can be reconstituted with varying ratios of carotenoids, consistent with our previous observation that the carotenoid to Chl ratio is substantially higher in P. cruentum grown under high irradiance. Also notable is that zeaxanthin does not act as an accessory light-harvesting pigment, even though it is highly likely that it occupies the position assigned to lutein in the CAB LHCs.