Euplotes crassus has genes encoding telomere-binding proteins and telomere-binding protein homologs.

We have identified two 1.6 kb macronuclear DNA molecules from Euplotes crassus that hybridize to the alpha subunit of the Oxytricha telomere protein. We have shown that one of these molecules encodes the 51 kDa Euplotes telomere protein while the other appears to encode a homolog of the telomere protein. Although this homolog clearly differs in sequence from the Euplotes telomere protein, the two proteins share extensive amino acid sequence identity with each other and with the alpha subunit of the Oxytricha telomere protein. In all three proteins 35-36% of the amino acids are identical, while 54-56% are similar. The most extended regions of sequence conservation map within the N-terminal section; this section has been shown to comprise the DNA-binding domain in the Euplotes telomere protein. Our findings suggest that some of the conserved amino acids may be involved in DNA recognition and binding. The gene encoding the telomere protein homolog contains two introns; one of these introns is only 24 bp in length. This is the smallest mRNA intron reported to date.     

Enhanced formaldehyde detoxification by overexpression of glutathione-dependent formaldehyde dehydrogenase from Arabidopsis

The ADH2 gene codes for the Arabidopsis glutathione-dependent formaldehyde dehydrogenase (FALDH), an enzyme involved in formaldehyde metabolism in eukaryotes. In the present work, we have investigated the potential role of FALDH in detoxification of exogenous formaldehyde. We have generated a yeast (Saccharomyces cerevisiae) mutant strain (sfa1Delta) by in vivo deletion of the SFA1 gene that codes for the endogenous FALDH. Overexpression of Arabidopsis FALDH in this mutant confers high resistance to formaldehyde added exogenously, which demonstrates the functional conservation of the enzyme through evolution and supports its essential role in formaldehyde metabolism. To investigate the role of the enzyme in plants, we have generated Arabidopsis transgenic lines with modified levels of FALDH. Plants overexpressing the enzyme show a 25% increase in their efficiency to take up exogenous formaldehyde, whereas plants with reduced levels of FALDH (due to either a cosuppression phenotype or to the expression of an antisense construct) show a marked slower rate and reduced ability for formaldehyde detoxification as compared with the wild-type Arabidopsis. These results show that the capacity to take up and detoxify high concentrations of formaldehyde is proportionally related to the FALDH activity in the plant, revealing the essential role of this enzyme in formaldehyde detoxification.     

A double residue substitution in the coenzyme-binding site accounts for the different kinetic properties between yeast and human formaldehyde dehydrogenases

Glutathione-dependent formaldehyde dehydrogenase (FALDH) is the main enzymatic system for formaldehyde detoxification in all eukaryotic and many prokaryotic organisms. The enzyme of yeasts and some bacteria exhibits about 10-fold higher k(cat) and K(m) values than those of the enzyme from animals and plants. Typically Thr-269 and Glu-267 are found in the coenzyme-binding site of yeast FALDH, but Ile-269 and Asp-267 are present in the FALDH of animals. By site-directed mutagenesis we have prepared the T269I and the D267E mutants and the D267E/T269I double mutant of Saccharomyces cerevisiae FALDH with the aim of investigating the role of these residues in the kinetics. The T269I and the D267E mutants have identical kinetic properties as compared with the wild-type enzyme, although T269I is highly unstable. In contrast, the D267E/T269I double mutant is stable and shows low K(m) (2.5 microM) and low k(cat) (285 min(-1)) values with S-hydroxymethylglutathione, similar to those of the human enzyme. Therefore, the simultaneous exchange at both residues is the structural basis of the two distinct FALDH kinetic types. The local structural perturbations imposed by the substitutions are suggested by molecular modeling studies. Finally, we have studied the effect of FALDH deletion and overexpression on the growth of S. cerevisiae. It is concluded that the FALDH gene is not essential but enhances the resistance against formaldehyde (0.3-1 mM). Moreover, the wild-type enzyme (with high k(cat) and K(m)) provides more resistance than the double mutant (with low k(cat) and K(m)).     

Binding linkage in a telomere DNA-protein complex at the ends of Oxytricha nova chromosomes

Alpha and beta protein subunits of the telomere end binding protein from Oxytricha nova (OnTEBP) combine with telomere single strand DNA to form a protective cap at the ends of chromosomes. We tested how protein-protein interactions seen in the co-crystal structure relate to DNA binding through use of fusion proteins engineered as different combinations of domains and subunits derived from OnTEBP. Joining alpha and beta resulted in a protein that bound single strand telomere DNA with high affinity (K(D-DNA)=1.4 nM). Another fusion protein, constructed without the C-terminal protein-protein interaction domain of alpha, bound DNA with 200-fold diminished affinity (K(D-DNA)=290 nM) even though the DNA-binding domains of alpha and beta were joined through a peptide linker. Adding back the alpha C-terminal domain as a separate protein restored high-affinity DNA binding. The binding behaviors of these fusion proteins and the native protein subunits are consistent with cooperative linkage between protein-association and DNA-binding equilibria. Linking DNA-protein stability to protein-protein contacts at a remote site may provide a trigger point for DNA-protein disassembly during telomere replication when the single strand telomere DNA must exchange between a very stable OnTEBP complex and telomerase.     

The effects of overexpression of formaldehyde dehydrogenase gene from Brevibacillus brevis on the physiological characteristics of tobacco under formaldehyde stress

The faldh gene encodes the Brevibacillus brevis glutathione-dependent formaldehyde dehydrogenase (FALDH), an enzyme involved in formaldehyde metabolism. In the present work, we have investigated the physiological characteristics of transgenic faldh tobacco under formaldehyde stress. Overexpression of B. brevis FALDH confers tobacco tolerance to high HCHO concentrations. The transgenic tobacco lines had the higher biomass, produced the higher content of total proteins and soluble sugars, the lower levels of MDA, protein carbonyl (PC), and H₂O₂ as compared with the wild-type tobacco under HCHO stress. The contents of chlorophyll (Chl), including Chl a, Chl b, and the ratio of Chl a/b, and the content of anthocyanidin in transgenic plants under HCHO stress were also higher than that in wild-type tobacco. These results show that high HCHO tolerance and changes of physiological characteristics related to stress tolerance were due to the overexpressing of FALDH in tobacco.     

The gene encoding glutathione-dependent formaldehyde dehydrogenase/GSNO reductase is responsive to wounding,jasmonic acid and salicylic acid

It has recently been discovered that glutathione-dependent formaldehyde dehydrogenase (FALDH) exhibits a strong S-nitrosoglutathione reductase activity. Plants use NO and S-nitrosothiols as signaling molecules to activate defense mechanisms. Therefore, it is interesting to investigate the regulation of FALDH by mechanical wounding and plant hormones involved in signal transduction. Our results show that the gene encoding FALDH in Arabidopsis (ADH2) is down-regulated by wounding and activated by salicylic acid (SA). In tobacco, FALDH levels and enzymatic activity decreased after jasmonate treatment, and increased in response to SA. This is the first time that regulation of FALDH in response to signals associated with plant defense has been demonstrated.     

甲醛氧化途径关键酶重组蛋白的生化特性及固定化酶吸收甲醛效果研究

甲醛脱氢酶(formaldehyde dehydrogenase,ADH)与甲酸脱氢酶(formate dehydrogenase,FDH)是甲醛氧化途径的两个关键酶.恶臭假单胞菌(Pseudomonas putida)的PADH是一种不依赖谷胱甘肽可以把游离甲醛直接氧化为甲酸的脱氢酶,博伊丁假丝酵母菌(Candida boidinii)的FDH在有NAD+存在时可以把甲酸氧化为二氧化碳.以基因组DNA为模板用PCR方法,从P.putida中扩增出PADH基因的编码区(padh),从C.boidinii中扩增出FDH的编码区(fdh),然后亚克隆到pET-28a(+)中分别构建这两个基因的原核表达载体pET-28a-padh和pET-28a-fdh,转化大肠杆菌,利用IPTG诱导重组蛋白PADH和FDH的表达.通过优化条件使重组蛋白的表达量占菌体总蛋白的70%以上,通过亲和层析法纯化出可溶性PADH和FDH重组蛋白.对重组蛋白的生化特性分析结果表明:PADH在最适反应温度50℃的活性为1.95 U/mg;FDH在最适反应温度40℃的活性为0.376 U/mg.所表达的重组蛋白与之前报道过的相比,具有更好的热稳定性和更广的温度适应范围.将PADH、FDH两个重组蛋白及辅因子NAD+固定到聚丙烯酰胺载体基质上,对固定化酶甲醛吸收效果的初步分析结果显示固定化酶对空气中的甲醛有一定的吸收效果,说明这两种酶被固定后具有开发成治理甲醛污染环保产品的潜力.     

Modification of intracellular levels of glutathione-dependent formaldehyde dehydrogenase alters glutathione homeostasis and root development

Glutathione (GSH)-dependent formaldehyde dehydrogenase (FALDH) is a highly conserved medium-chain dehydrogenase reductase and the main enzyme that metabolizes intracellular formaldehyde in eukaryotes. It has been recently shown that it exhibits a strong S-nitrosoglutathione (GSNO) reductase activity and could be a candidate to regulate NO-signalling functions. However, there is a lack of knowledge about the tissue distribution of this enzyme in plants. Here, we have studied the localization and developmental expression of the enzyme using immunolocalization and histochemical activity assay methods. We conclude that FALDH is differentially expressed in the organs of Arabidopsis thaliana mature plants, with higher levels in roots and leaves from the first stages of development. Spatial distribution of FALDH in these two organs includes the main cell types [epidermis (Ep) and cortex (Cx) in roots, and mesophyll in leaves] and the vascular system. Arabidopsis thaliana mutants with modified levels of FALDH (both by over- and under-expression of the FALDH-encoding gene) show a significant reduction of root length, and this phenotype correlates with an overall decrease of intracellular GSH levels and alteration of spatial distribution of GSH in the root meristem. Tansgenic roots are partially insensitive to exogenous GSH, suggesting an inability to detect reduction-oxidation (redox) changes of the GSH pool and/or maintain GSH homeostasis.     

Phosphorylation of the Oxytricha telomere protein: possible cell cycle regulation.

In the macronucleus of the ciliate Oxytricha nova, telomeres end with single-stranded (T4G4)2 DNA bound to a heterodimeric telomere protein (alpha beta). Both the alpha and beta subunits (alpha-TP and beta-TP) were phosphorylated in asynchronously growing Oxytricha; beta-TP was phosphorylated to a much higher degree. In vitro, mouse cyclin-dependent kinases (Cdks) phosphorylated beta-TP in a lysine-rich domain that is not required for specific DNA binding but is implicated in higher order structure formation of telomeres. Therefore, phosphorylation of beta-TP could modulate a function of the telomere protein that is separate from specific DNA binding. Phosphoamino acid analysis revealed that the mouse Cdks modify predominantly threonine residues in beta-TP, consistent with the observation that beta-TP contains two consensus Cdk recognition sequences containing threonine residues. In Xenopus egg extracts that undergo cell cycling, beta-TP was phosphorylated in M phase and dephosphorylated in interphase. This work provides the first direct evidence of phosphorylation at telomeres in any organism, as well as indirect evidence for cell cycle regulation of telomere phosphorylation. The Cdc2/cyclin A and Cdc2/cyclin B kinases are required for major mitotic events. An attractive model is that phosphorylation of beta-TP by these kinases is required for the breakdown of telomere associations with each other and/or with nuclear structures prior to nuclear division.     

A transcriptional fusion of genes encoding glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and enolase in dinoflagellates

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and enolase are enzymes essential for glycolysis and gluconeogenesis. Dinoflagellates possess several types of both GAPDH and enolase genes. Here, we identify a novel cytosolic GAPDH-enolase fusion protein in several dinoflagellate species. Phylogenetic analyses revealed that the GAPDH moiety of this fusion is weakly related to a cytosolic GAPDH previously reported in dinoflagellates, ciliates, and an apicomplexan. The enolase moiety has phylogenetic affinity with sequences from ciliates and apicomplexans, as expected for dinoflagellate genes. Furthermore, the enolase moiety has two insertions in a highly conserved region of the gene that are shared with ciliate and apicomplexan homologues, as well as with land plants, stramenopiles, haptophytes, and a chlorarachniophyte. Another glycolytic gene fusion in eukaryotes is the mitochondrion-targeted triose-phosphate isomerase (TPI) and GAPDH fusion in stramenopiles (i.e. diatoms and oomycetes). However, unlike the mitochondrial TPI-GAPDH fusion, the GAPDH-enolase fusion protein appears to exist in the same compartment as stand-alone homologues of each protein, and the metabolic reactions they catalyze in glycolysis and gluconeogenesis are not directly sequential. It is possible that the fusion is post-translationally processed to give separate GAPDH and enolase products, or that the fusion protein may function as a single bifunctional polypeptide in glycolysis, gluconeogenesis, or perhaps more likely in some previously unrecognized metabolic capacity.     

Fatty aldehyde dehydrogenase: genomic structure, expression and mutation analysis in Sjögren-Larsson syndrome

Fatty aldehyde dehydrogenase (FALDH) is a microsomal enzyme that catalyzes the oxidation of medium- and long-chain aliphatic aldehydes derived from metabolism of fatty alcohol, phytanic acid, ether glycerolipids and leukotriene B4. The FALDH gene (ALDH3A2) in man and mouse consists of 11 exons and is closely linked to the gene for ALDH3. In both species, alternative splicing results in formation of a second minor protein, FALDHv, that has a unique carboxy-terminal end. The functional significance of this alternate protein is not known. In humans, mutations in the FALDH gene cause Sj?gren-Larsson syndrome (SLS), which is characterized by ichthyosis, mental retardation and spasticity. Missense mutations involving 24 amino acid positions in FALDH have been identified. These amino acids are more highly conserved among related class 3 aldehyde dehydrogenase enzymes than expected, suggesting that they are critically important for protein folding, catalysis or stability. Studies of mutations in SLS should prove useful for understanding structure-function correlations in FALDH and other aldehyde dehydrogenase proteins.     

In Vivo Analysis of the Major Exocytosis-sensitive Phosphoprotein in Tetrahymena

Phosphoglucomutase (PGM) is a ubiquitous highly conserved enzyme involved in carbohydrate metabolism. A number of recently discovered PGM-like proteins in a variety of organisms have been proposed to function in processes other than metabolism. In addition, sequence analysis suggests that several of these may lack PGM enzymatic activity. The best studied PGM-like protein is parafusin, a major phosphoprotein in the ciliate Paramecium tetraurelia that undergoes rapid and massive dephosphorylation when cells undergo synchronous exocytosis of their dense-core secretory granules. Indirect genetic and biochemical evidence also supports a role in regulated exocytotic membrane fusion. To examine this matter directly, we have identified and cloned the parafusin homologue in Tetrahymena thermophila, a ciliate in which protein function can be studied in vivo. The unique T. thermophila gene, called PGM1, encodes a protein that is closely related to parafusin by sequence and by characteristic post-translational modifications. Comparison of deduced protein sequences, taking advantage of the known atomic structure of rabbit muscle PGM, suggests that both ciliate enzymes and all other PGM-like proteins have PGM activity. We evaluated the activity and function of PGM1 through gene disruption. Surprisingly, ΔPGM1 cells displayed no detectable defect in exocytosis, but showed a dramatic decrease in PGM activity. Both our results, and reinterpretation of previous data, suggest that any potential role for PGM-like proteins in regulated exocytosis is unlikely to precede membrane fusion.     

Sequence of the small subunit ribosomal RNA gene from the hypotrichous ciliate Euplotes aediculatus

We have determined the complete nucleotide sequence of the coding region of the small subunit rRNA gene of the hypotrichous ciliate Euplotes aediculatus. It is 1882 nucleotides long and contains several inserts not present in the small subunit rRNA genes of the hypotrichs Oxytricha nova and Stylonychia pustulata. A comparison of the sequences suggests that E. aediculatus is much less closely related to these other two hypotrichs than they are to each other. Although the gene sequence of E. aediculatus is drifting more rapidly than those of these other two species, its faster evolutionary clock is not enough to account for the degree of difference between them.     

Ac23, an envelope fusion protein homolog in the baculovirus Autographa californica multicapsid nucleopolyhedrovirus,is a viral pathogenicity factor

Viral envelope fusion proteins are important structural proteins that mediate viral entry and may affect or determine the host range of a virus. The acquisition, exchange, and evolution of such envelope proteins may dramatically affect the success and evolutionary divergence of viruses. In the family Baculoviridae, two very different envelope fusion proteins have been identified. Budded virions of group I nucleopolyhedroviruses (NPVs) such as the Autographa californica multicapsid nucleopolyhedrovirus (AcMNPV), contain the essential GP64 envelope fusion protein. In contrast group II NPVs and granuloviruses have no gp64 gene but instead encode a different envelope protein called F. F proteins from group II NPVs can functionally substitute for GP64 in gp64null AcMNPV viruses, indicating that GP64 and these F proteins serve a similar functional role. Interestingly, AcMNPV (and other gp64-containing group I NPVs) also contain an F gene homolog (Ac23) but the AcMNPV F homolog cannot compensate for the loss of gp64. In the present study, we show that Ac23 is expressed and is found in budded virions. To examine the function of F protein homologs from the gp64-containing baculoviruses, we generated an Ac23null AcMNPV genome by homologous recombination in E. coli. We found that Ac23 was not required for viral replication or pathogenesis in cell culture or infected animals. However, Ac23 accelerated the mortality of infected insect hosts by approximately 28% or 26 h. Thus, Ac23 represents an important viral pathogenicity factor in larvae infected with AcMNPV.     

Characterization of a novel fibronectin-binding surface protein in group A streptococci

Streptococcus pyogenes interacts with host fibronectin via distinct surface components. One of these components is the Sfbl protein (streptococcal fibronectin-binding protein, now specified as class I), an adhesin that represents a protein family with characteristic features. Here we present the complete structure of a novel fibronectin-binding protein of S. pyogenes , designated SfbII, which is distinct from the previously described Sfbl proteins. The sfbII gene originated from a λ EMBL3 library of chromosomal DNA from group A streptococcal strain A75 and coded for a 113kDa protein exhibiting features of membrane-anchored surface proteins of Gram-positive cocci. The expression of biologically active fusion proteins allowed the determination of the location of the fibronectin-binding domain within the C-terminal part of the protein. It consisted of two and a half repeats which share common motifs with fibronectin-binding repeats of other streptococcal and staphylococcal proteins. Purified recombinant fusion protein containing this domain competitively inhibited the binding of fibronectin to the parental S. pyogenes strain. Furthermore, polyclonal antibodies against the binding domain specifically blocked the Sfbll receptor site on the streptococcal surface. No cross-reactivity could be detected between anti-Sfbll antibodies and the sfbl gene product, and vice versa, indicating that the two proteins do not share common immunogenic epitopes. Southern hybridization experiments performed with specific sfbll gene probes revealed the presence of the sfbll gene in more than 55% of 93 streptococcal isolates tested. The majority of the strains also harboured the sfbl gene, and 86% carried at least one of the two sfb genes.     

Identification of a novel gene, DZIP (DAZ-interacting protein), that encodes a protein that interacts with DAZ (deleted in azoospermia) and is expressed in embryonic stem cells and germ cells

Evidence from diverse organisms, including humans, suggests that the DAZ (Deleted in Azoospermia) gene and a closely related homolog, DAZL (DAZ-like), are required early in germ cell development to maintain initial germ cell populations. Here we report the identification and characterization of the DZIP (DAZ-Interacting Protein) gene, which encodes at least three different protein isoforms that contain a C2H2 zinc-finger domain. The DZIP gene is expressed predominantly in human embryonic stem cells and fetal and adult germ cells; moreover, two DZIP protein isoforms colocalize with DAZ and/or DAZL proteins in these tissues. Finally, we provide evidence indicating that DZIP may associate with DAZ and its other cofactors in an RNA-binding protein complex that functions in both ES cells and germ cells.     

MLL targets SET domain methyltransferase activity to Hox gene promoters

MLL, the human homolog of Drosophila trithorax, maintains Hox gene expression in mammalian embryos and is rearranged in human leukemias resulting in Hox gene deregulation. How MLL or MLL fusion proteins regulate gene expression remains obscure. We show that MLL regulates target Hox gene expression through direct binding to promoter sequences. We further show that the MLL SET domain is a histone H3 lysine 4-specific methyltransferase whose activity is stimulated with acetylated H3 peptides. This methylase activity is associated with Hox gene activation and H3 (Lys4) methylation at cis-regulatory sequences in vivo. A leukemogenic MLL fusion protein that activates Hox expression had no effect on histone methylation, suggesting a distinct mechanism for gene regulation by MLL and MLL fusion proteins.     

Fatty aldehyde dehydrogenase: genomic structure,expression and mutation analysis in Sjögren–Larsson syndrome

Fatty aldehyde dehydrogenase (FALDH) is a microsomal enzyme that catalyzes the oxidation of medium- and long-chain aliphatic aldehydes derived from metabolism of fatty alcohol, phytanic acid, ether glycerolipids and leukotriene B4. The FALDH gene (ALDH3A2) in man and mouse consists of 11 exons and is closely linked to the gene for ALDH3. In both species, alternative splicing results in formation of a second minor protein, FALDHv, that has a unique carboxy-terminal end. The functional significance of this alternate protein is not known. In humans, mutations in the FALDH gene cause Sjögren–Larsson syndrome (SLS), which is characterized by ichthyosis, mental retardation and spasticity. Missense mutations involving 24 amino acid positions in FALDH have been identified. These amino acids are more highly conserved among related class 3 aldehyde dehydrogenase enzymes than expected, suggesting that they are critically important for protein folding, catalysis or stability. Studies of mutations in SLS should prove useful for understanding structure–function correlations in FALDH and other aldehyde dehydrogenase proteins.     

The serine/arginine-rich protein family in rice plays important roles in constitutive and alternative splicing of pre-mRNA

Ser/Arg-rich (SR) proteins play important roles in the constitutive and alternative splicing of pre-mRNA. We isolated 20 rice (Oryza sativa) genes encoding SR proteins, of which six contain plant-specific characteristics. To determine whether SR proteins modulate splicing efficiency and alternative splicing of pre-mRNA in rice, we used transient assays in rice protoplasts by cotransformation of SR protein genes with the rice Waxy(b) (Wx(b))-beta-glucuronidase fusion gene. The results showed that plant-specific RSp29 and RSZp23, an SR protein homologous to human 9G8, enhanced splicing and altered the alternative 5' splice sites of Wx(b) intron 1. The resulting splicing pattern was unique to each SR protein; RSp29 stimulated splicing at the distal site, and RSZp23 enhanced splicing at the proximal site. Results of domain-swapping experiments between plant-specific RSp29 and SCL26, which is a homolog of human SC35, showed the importance of RNA recognition motif 1 and the Arg/Ser-rich (RS) domain for the enhancement of splicing efficiencies. Overexpression of plant-specific RSZ36 and SRp33b, a homolog of human ASF/SF2, in transgenic rice changed the alternative splicing patterns of their own pre-mRNAs and those of other SR proteins. These results show that SR proteins play important roles in constitutive and alternative splicing of rice pre-mRNA.     

Evolutionary origins and functions of the carotenoid biosynthetic pathway in marine diatoms

Carotenoids are produced by all photosynthetic organisms, where they play essential roles in light harvesting and photoprotection. The carotenoid biosynthetic pathway of diatoms is largely unstudied, but is of particular interest because these organisms have a very different evolutionary history with respect to the Plantae and are thought to be derived from an ancient secondary endosymbiosis between heterotrophic and autotrophic eukaryotes. Furthermore, diatoms have an additional xanthophyll-based cycle for dissipating excess light energy with respect to green algae and higher plants. To explore the origins and functions of the carotenoid pathway in diatoms we searched for genes encoding pathway components in the recently completed genome sequences of two marine diatoms. Consistent with the supplemental xanthophyll cycle in diatoms, we found more copies of the genes encoding violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP) enzymes compared with other photosynthetic eukaryotes. However, the similarity of these enzymes with those of higher plants indicates that they had very probably diversified before the secondary endosymbiosis had occurred, implying that VDE and ZEP represent early eukaryotic innovations in the Plantae. Consequently, the diatom chromist lineage likely obtained all paralogues of ZEP and VDE genes during the process of secondary endosymbiosis by gene transfer from the nucleus of the algal endosymbiont to the host nucleus. Furthermore, the presence of a ZEP gene in Tetrahymena thermophila provides the first evidence for a secondary plastid gene encoded in a heterotrophic ciliate, providing support for the chromalveolate hypothesis. Protein domain structures and expression analyses in the pennate diatom Phaeodactylum tricornutum indicate diverse roles for the different ZEP and VDE isoforms and demonstrate that they are differentially regulated by light. These studies therefore reveal the ancient origins of several components of the carotenoid biosynthesis pathway in photosynthetic eukaryotes and provide information about how they have diversified and acquired new functions in the diatoms.