The primary structure of spinach acyl carrier protein

Spinach holo-acyl carrier protein: overproduction and phosphopantetheinylation in Escherichia coli BL21(DE3), in vitro acylation, and enzymatic desaturation of histidine-tagged isoform I

Spinach ACP isoform I was overexpressed in Escherichia coli BL21(DE3) using a gene synthesized from codons associated with high-level expression in E. coli. The synthetic gene has extensive changes in codon usage (23 of 77 total codons) relative to that of the originally synthesized plant gene (P. D. Beremand et al., 1987, Arch. Biochem. Biophys. 256, 90-100). After expression of the new synthetic gene, purified ACP and ACP-His6 were obtained in yields of up to 70 mg L-1 of culture medium, compared to approximately 1-6 mg L-1 of purified ACP obtained from the gene composed of predicted spinach codons. In either shaken flask or fermentation culture, approximately 15% conversion to holo-ACP or holo-ACP-His6 was obtained regardless of the level of protein expression. However, coexpression of ACP-His6 with E. coli holo-ACP synthase in E. coli BL21(DE3) during pH- and dissolved O2-controlled fermentation routinely yielded greater than 95% conversion to holo-ACP-His6. Electrospray ionization mass spectrometric analysis of the purified recombinant ACPs revealed that the amino terminal Met was efficiently removed, but only if the bacterial cell lysates were prepared in the absence of EDTA. This observation is consistent with the inhibition of endogenous Met-aminopeptidase by removal of catalytically essential Co(II) and introduces the importance of considering the catalytic properties of host enzymes providing ad hoc posttranslational modification of recombinant proteins. Stearoyl-ACP-His6 was shown to be indistinguishable from stearoyl-ACP as a substrate for enzymatic acylation and desaturation. In combination, these studies provide a coordinated scheme to produce and characterize quantities of acyl-ACPs sufficient to support expanded biophysical and structural studies.

Malonyl-coenzyme A:acyl carrier protein acyltransferase of Streptomyces glaucescens: a possible link between fatty acid and polyketide biosynthesis

Streptomyces glaucescens, a Gram-positive soil bacterium, produces the polyketide antibiotic tetracenomycin (Tcm) C. To study possible biochemical connections between the biosynthesis of bacterial fatty acids and polyketides, the abundant acyl carrier protein (ACP) detected throughout the growth of the tetracenomycin (Tcm) C-producing S. glaucescens was purified to homogeneity and found to behave like many other ACPs from bacteria and plants (apparent M(r) of 20,000 on gel filtration chromatography, apparent M(r) of 3400-4800 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing conditions, and pI approximately 3.8). By using an oligodeoxynucleotide synthesized in accordance with the sequence of residues 25-36 of the ACP, the fabC gene encoding this protein was cloned, and expression of this gene in Escherichia coli yielded the ACP entirely as the active holoenzyme. Sequence analysis of 4.3 kilobases (kb) of DNA flanking fabC revealed the presence of three other genes oriented in the same transcriptional direction in the order fabD, fabH, fabC, and fabB. Each of the four genes is predicted to encode proteins with high sequence similarity to the following components of the E. coli fatty acid synthase (FAS): the FabD malonyl-coenzyme A:ACP acyltransferase (MAT), FabH 3-oxoacyl:ACP synthase III, AcpP ACP, and FabB 3-oxoacyl:ACP synthase I. Expression of the S. glaucescens fabD gene in E. coli produced active MAT able to catalyze in vitro the transfer of radioactive malonate from malonyl-coenzyme A to the E. coli AcpP and S. glaucescens FabC ACPs, as well as to the TcmM ACP component of the Tcm type II polyketide synthase [Shen, B., et al. (1992) J. Bacteriol 174, 3818-3821]. Expression of fabD also restored the high-temperature growth of the E. coli fabD89 mutant that bears a temperature-sensitive MAT. The latter finding and the close similarity between the organization of the S. glaucescens fabDHCB and E. coli FAS-encoding genes (fabH/fabD/fabG/acpP/fabF) suggest that the S. glaucescens genes encode FAS enzymes. Moreover, on the basis of its in vitro activity, it is possible that the S. glaucescens FabD MAT is responsible for charging the TcmM ACP with malonate in vivo, a key step in the synthesis of the deca(polyketide) precursor of Tcm C. This implies the existence of a functional connection between fatty acid and polyketide metabolism in this bacterium.

The isolation and functional characterisation of a B. napus acyl carrier protein 5' flanking region involved in the regulation of seed storage lipid synthesis

Acyl carrier protein (ACP) is a key component of the fatty acid biosynthetic machinery in plants. A 1.4 kb 5' flanking region of a Brassica napus ACP gene (ACP05) was transcriptionally fused to the reporter gene beta-glucuronidase (GUS), and expression of the chimeric gene monitored in transgenic tobacco. GUS activity was found to increase through seed development reaching a maximum value, coincident with the most active phase of storage lipid synthesis that was, on average, 100-fold higher than that observed in leaf. In control plants transformed with CaMV 35S-GUS constructs, GUS activity was similar in leaf and all stages of seed development. Based on average values, the level of GUS expression obtained via the ACP promoter was comparable to that obtained from the CaMV 35S promoter. We therefore conclude that the isolated 5' ACP flanking sequence represents a strong promoter element involved in the developmental regulation of storage lipid synthesis in B. napus seed tissue. Putative regulatory elements in the 5' upstream region of ACP05 were identified by dot matrix analysis and by sequence comparison with the upstream regions from a second seed-expressed rape ACP gene and from an Arabidopsis ACP gene.

Molecular structure of the multifunctional fatty acid synthetase gene of Brevibacterium ammoniagenes: its sequence of catalytic domains is formally consistent with a head-to-tail fusion of the two yeast genes FAS1 and FAS2

The Brevibacterium ammoniagenes fatty acid synthetase (FAS) gene was isolated from a series of overlapping clones by both immunological and plaque hybridization screening of two independent gene libraries. From the isolated DNA a contiguous segment of 10,549 bp was sequenced in both directions. The sequenced DNA contained a very long (9312 nucleotides) open reading frame coding for a protein of 3104 amino acids and with a molecular mass of 327,466 daltons. Based on characteristic sequence motifs known from other FAS systems, seven different FAS active centres were identified at distinct locations within the polypeptide chain. Only one component enzyme, the 3-hydroxydecanoyl beta, gamma-dehydratase, has not yet been localized definitively within the gene. Translation is presumed to start from a GUG triplet located 25 nucleotides downstream of the transcriptional initiation site. There is a canonical Shine-Dalgarno sequence just before this start codon. Comparison of the B. ammoniagenes FAS sequence with those of other known fatty acid synthetases revealed a particularly high degree of similarity to the products of the two yeast genes, FAS1 and FAS2 (30% identical and 46% identical plus closely related amino acids). This similarity extends over the entire length of the genes and involves not only the primary sequences of individual component enzymes but also their sequential order within the multifunctional proteins. These data, together with those on the structure of other fatty acid synthetases, are interpreted in terms of a contribution of both primary structure and subunit cooperation to a conserved topology of functional domains common to all type I FAS complexes.

The plastid genome of Cryptomonas phi encodes an hsp70-like protein, a histone-like protein, and an acyl carrier protein

The plastid genome of Cryptomonas phi, a cryptomonad alga, contains three genes that have not previously been found in any organellar genome. Each of these genes encodes a functional class of organellar gene product not previously reported. The first gene, dnaK, encodes a polypeptide of the hsp70 heat shock protein family. The predicted amino acid sequence of the DnaK protein is 54% identical to that of the Escherichia coli hsp70 protein (DnaK), 50-53% identical to that of two nucleus-encoded mitochondrial hsp70 proteins, and 43-46% identical to that of several eukaryotic cytoplasmic members of the hsp70 protein family. The second gene, hlpA, encodes a polypeptide resembling bacterial histone-like proteins. The predicted amino acid sequence of the HlpA protein is 25-53% identical to that of several bacterial histone-like proteins, and the identity increases to 39-76% over a conserved region corresponding to the long arm that binds DNA. The third gene, acpA, encodes an acyl carrier protein, which is a key cofactor in the synthesis and metabolism of fatty acids. Its predicted amino acid sequence is 36-59% identical to that of eubacterial and plant chloroplast (nucleus-encoded) acyl carrier proteins.

The barley genes Acl1 and Acl3 encoding acyl carrier proteins I and III are located on different chromosomes

Acyl carrier protein (ACP) is an essential cofactor for plant fatty acid synthesis. Three isoforms occur in barley seedling leaves. The genes Acl1 and Acl3 coding for the predominant ACP I and the minor ACP III, respectively, have been cloned and characterized as has a full-length cDNA for ACP III. Both genes, extending over more than 2.5 kb, have a conserved mosaic structure of four exons and three introns which result in mRNAs of ca. 900 bases. Alignment of the DNA sequences demonstrates that homology is restricted to the two exons coding for the mature protein whereas the remaining segments of the genes including the transit peptide-coding domains lack homology. Southern blot analyses demonstrate that Acl1 and Acl3 represent single copy genes located on chromosomes 7 and 1, respectively. Primer extension analyses identified multiple transcription start sites in both genes. The promoter regions are remarkably different; that of Acl3 resembles those for mammalian housekeeping genes in having a high G + C content plus three copies of an RNA polymerase II recognition GC element and in lacking correctly positioned TATA boxes. These features are in accordance with the hypothesis that Acl1 is specifically expressed in leaf tissue whereas Acl3 is a constitutively expressed gene.

The acyl-carrier protein in Neurospora crassa mitochondria is a subunit of NADH:ubiquinone reductase (complex I)

We determined the primary structure of a 9.6-kDa subunit of the respiratory chain NADH:ubiquinone reductase (complex I) from Neurospora crassa mitochondria and found a close relationship between this subunit and the bacterial or chloroplast acyl-carrier protein. The degree of sequence identity amounts to 80% in a region of 19 residues around the serine to which the phosphopantetheine is bound. The N-terminal presequence of the subunit has the characteristic features of a mitochondrial import sequence. We cultivated the auxotroph pan-2 mutant of N. crassa in the presence of [14C]pantothenate and recovered all radioactivity incorporated into mitochondrial protein in the 9.6-kDa subunit of complex I. We cultivated N. crassa in the presence of chloramphenicol to accumulate the nuclear-encoded peripheral arm of complex I. This pre-assembled arm also contains the 9.6-kDa subunit. These results demonstrate that an acyl-carrier protein with pantothenate as prosthetic group is a constituent part of complex I in N. crassa.

6-Hydroxymellein synthetase as a multifunctional enzyme complex in elicitor-treated carrot root extract

Synthetic activity of a polyketide compound 6-hydroxymellein was induced in elicitor-treated carrot root tissues. The activity was significantly inhibited by an antiserum raised against the acyl carrier protein (ACP) of fatty acid synthetase, suggesting that the enzyme(s) for 6-hydroxymellein synthesis require(s) a functional unit similar to ACP. However, the synthetic activity was not stimulated by the addition of ACP purified from Escherichia coli and was not lost even after fractionation by gel-filtration chromatography. The active fraction obtained by gel-filtration (136 kDa) was subjected to immunoblot analysis, and a 128 kDa polypeptide in the fraction was found to cross-react with anti-ACP serum. These observations suggest that the biosynthesis of 6-hydroxymellein in carrot cells is catalyzed by an enzyme consisting of a single peptide chain.

Purification and characterization of acyl carrier protein from two cyanobacteria species

The acyl carrier protein (ACP), an essential protein cofactor for fatty acid synthesis, has been isolated from two cyanobacteria: the filamentous, heterocystous, Anabaena variabilis (ATCC 29211) and the unicellular Synechocystis 6803 (ATCC 27184). Both ACPs have been purified to homogeneity utilizing a three-column procedure. Synechocystis 6803 ACP was purified 1800-fold with 67% yield, while A. variabilis ACP was purified 1040-fold with 50% yield. Yields of 13.0 micrograms ACP/g Synechocystis 6803 and 9.0 micrograms ACP/g A. variabilis were achieved. Amino acid analysis indicated that these ACPs were highly charged acidic proteins similar to other known ACPs. Sequence analysis revealed that both cyanobacterial ACPs were highly conserved with both spinach and Escherichia coli ACP at the phosphopantetheine prosthetic group region. Examining the probability of alpha-helix and beta-turn regions in various ACPs, showed that cyanobacterial ACPs were more closely related to E. coli ACP than spinach ACP I. Immunoblot analysis and a competitive binding assay for ACP illustrated that both ACPs bound poorly to spinach ACP I antibody. SDS/PAGE and native PAGE of Synechocystis 6803 ACP and A. variabilis ACP showed that cyanobacteria ACPs co-migrated with E. coli ACP and had relative molecular masses of 18,100 and 17,900 respectively. Both native and urea gel analysis of acyl-ACP products from fatty acid synthase reactions demonstrated that bacterial ACPs and plant ACP gave essentially the same metabolic products when assayed using either bacterial or plant fatty acid synthase. A. variabilis and Synechocystis 6803 ACP could be acylated using E. coli acyl ACP synthetase.

The multifunctional 6-methylsalicylic acid synthase gene of Penicillium patulum. Its gene structure relative to that of other polyketide synthases

6-Methylsalicylic acid synthase (MSAS) from Penicillium patulum is a homomultimer of a single, multifunctional protein subunit. The enzyme is induced, at the transcriptional level, during the end of the logarithmic growth phase. After approximately 150-fold purification, a homogeneous enzyme preparation was obtained exhibiting, upon SDS gel electrophoresis, a subunit molecular mass of 188 kDa. By immunological screening of a genomic P. patulum DNA expression library, the MSAS gene together with its flanking sequences was isolated; 7131 base pairs of the cloned genomic DNA were sequenced. Within this sequence the MSAS gene was identified as a 5322-bp-long open reading frame coding for a protein of 1774 amino acids and 190,731 Da molecular mass. Transcriptional initiation and termination sites were determined both by primer extension studies and from cDNA sequences specially prepared for the 5' and 3' portions of the gene. The same cDNA sequences revealed the presence of a 69-bp intron within the N-terminal part of the MSAS gene. The intron contains the canonical GT and AG dinucleotides at its 5'- and 3'-splice junctions. An internal TACTGAC sequence, resembling the TACTAAC consensus element of Saccharomyces cerevisiae introns is suggested to represent the branch point of the lariat splicing intermediate. When compared to other known polyketide synthases, distinct amino acid sequence similarities of limited lengths were observed with some, though not all, of them. A comparatively low degree of similarity was detected to the yeast and Penicillium FAS or to the plant chalcone and resveratrol synthases. In contrast, a significantly higher sequence similarity was found between MSAS and the rat fatty acid synthase, especially at their transacylase, 2-oxoacyl reductase, 2-oxoacyl synthase and acyl carrier protein domains. Besides several dissimilar, interspersed regions probably coding for MSAS- and FAS-specific functions, the sequential order of the similar domains was colinear in both enzymes. The low similarity between the two P. patulum polyketide synthases, MSAS and FAS, possibly supports a convergent rather than a divergent evolution of both multienzyme proteins.

Isolation and characterization of the constitutive acyl carrier protein from Rhizobium meliloti

Rhizobium species produce an inducible acyl carrier protein (ACP), encoded by the nodF gene, that somehow functions in an exchange of cell signals between bacteria and specific plant hosts, leading to nodulation of plant roots and symbiotic nitrogen fixation, as well as a constitutive ACP needed for the synthesis of essential cell lipids. The periplasmic cyclic glucans of Rhizobium spp. are also involved in specific rhizobium-plant interaction. These glucans are strongly similar to the periplasmic membrane-derived oligosaccharides (MDO) of Escherichia coli. E. coli ACP is an essential component of a membrane-bound transglucosylase needed for the biosynthesis of MDO, raising the possibility that either or both of the rhizobial ACPs might have a similar function. We have now isolated the constitutive ACP of R. meliloti and determined its primary structure. We have also examined its function, together with those of ACPs from E. coli, Rhodobacter sphaeroides, and spinach, in the MDO transglucosylase system and as substrate for the E. coli ACP acylase enzyme. All four ACPs act as acceptors of acyl residues, but only the E. coli ACP functions in the transglucosylase system.

Motional effects on NMR structural data. Comparison of spinach and Escherichia coli acyl carrier proteins

Proteins in solution need not exist in a single rigid structure but can exist in a dynamic equilibrium among structural forms. The problems that this poses for structure determination using nuclear Overhauser effect data from two-dimensional NMR experiments are discussed and illustrated with data on functionally equivalent proteins from two different species. One of these proteins, acyl carrier protein from Escherichia coli, shows a single set of resonances, easily interpreted on the basis of a single rigid structure. However, the related protein, acyl carrier protein from spinach, shows two sets of resonances, suggesting that two conformers in dynamic equilibrium would be a better structural model.

Evolutionary and tissue-specific control of expression of multiple acyl-carrier protein isoforms in plants and bacteria

We have examined the occurrence of multiple acyl-carrier protein (ACP), isoforms in evolutionarily diverse species of higher and lower plants. Isoforms were resolved by native polyacrylamide gel electrophoresis (PAGE), and were detected by Western blotting or fluorography of [(3)H]-palmitate-labelled ACPs. Multiple isoforms of ACP were found in leaf tissue of the monocotyledons Avena sativa and Hordeum vulgare and dicotyledons Arabidopsis thaliana, Cuphea wrightii, and Brassica napus. Lower vascular plants including the lycopod Selaginella krausseriana, the gymnosperms Ephedra sp. and Dioon edule, the ferns Davallia feejensis and Marsilea sp. and the most primitive known extant vascular plant, Psilotum nudum, were all found to have multiple ACP isoforms, as were the nonvascular liverworts, Lunularia sp. and Marchantia sp. and the moss, Polytrichum sp. Therefore, the development of ACP isoforms appears to have occurred early in plant evolution. However, we could detect only a single electrophoretic form of ACP in the unicellular algae Chlamydomonas reinhardtii and Dunaliella tertiolecta and the photosynthetic cyanobacteria Synechocystis strain 6803 and Agmnellum quadruplicatum. Thus, multiple forms of ACP do not occur in all photosynthetic organisms but may be associated with multicellular plants. We have also examined tissue specificity and light control over the expression of ACP isoforms. The relative abundance of multiple forms of ACP in leaf of Spinacia and Avena was altered very little by light. Rather, the different patterns of ACP isoforms were primarily dependent on the tissue type.

Complete amino acid sequence of chicken liver acyl carrier protein derived from the fatty acid synthase

The acyl carrier protein domain of the chicken liver fatty acid synthase has been isolated after tryptic treatment of the synthase. The isolated domain functions as an acceptor of acetyl and malonyl moieties in the synthase-catalyzed transfer of these groups from their coenzyme A esters and therefore indicates that the acyl carrier protein domain exists in the complex as a discrete entity. The amino acid sequence of the acyl carrier protein was derived from analyses of peptide fragments produced by cyanogen bromide cleavage and trypsin and Staphylococcus aureus V8 protease digestions of the molecule. The isolated acyl carrier protein domain consists of 89 amino acid residues and has a calculated molecular weight of 10,127. The protein contains the phosphopantetheine group attached to the serine residue at position 38. The isolated acyl carrier protein peptide shows some sequence homology with the acyl carrier protein of Escherichia coli, particularly in the vicinity of the site of phosphopantetheine attachment, and shows extensive sequence homology with the acyl carrier protein from the uropygial gland of goose.

Rat mammary gland fatty acid synthase: localization of the constituent domains and two functional polyadenylation/termination signals in the cDNA

The rat fatty acid synthase (FAS) is active only as a dimer, although the eight component functions are contained in a single polypeptide chain. Using mRNA from lactating rat mammary glands a cDNA expression library was established. With the overlapping immunologically positive clones we have an 8.9kb cDNA sequence for rat FAS. In the 3'-nontranslated region of the rat FAS cDNA we find a prototype polyadenylation/termination signal and 779 nucleotides upstream, a mutated one. Both of these polyadenylation/termination signals are used and give rise to two equally abundant mRNA species which are coordinately regulated. In the derived amino acid sequence we could locate six of the eight component functions; their order is NH2- beta-ketoacyl synthase - acetyl/malonyl transferases -enoyl reductase - acyl carrier protein - thioesterase -COOH. Comparison of FAS from different sources shows that the primary sequence is conserved only for the active residues and the amino acids in their immediate vicinity.

Amino acid sequences of substrate-binding sites in chicken liver fatty acid synthase

The amino acid sequences of three essential regions of chicken liver fatty acid synthase have been determined: that around 4'-phosphopantetheine ("carrier" site), the substrate "loading" site containing serine, and a "waiting" site for the growing fatty acid containing cysteine. The amino acid sequence of the 4'-phosphopantetheine region was determined for the acetyl-, malonyl-, hydroxybutyryl-, and butyryl-enzyme with peptides obtained by hydrolysis of the enzyme with trypsin and Staphylococcus aureus (V8) protease. The sequence region around the essential serine was obtained for the acetyl- and malonyl-enzyme. The N-terminus of the tryptic peptide was blocked. However, the same sequence is obtained for the acetyl- and malonyl-peptide after S. aureus protease digestion, suggesting that the enzyme contains a single acyl transferase rather than two separate transacylases. The sequence around the cysteine was obtained by use of a radioactive iodoacetamide label. An unusual sequence of three serines adjacent to the cysteine was found. The strong similarities between peptides from different species for all three of the regions suggest that the multifunctional polypeptides from yeast and animals have evolved from the monofunctional enzymes of lower species.

Plastid-localised seed acyl-carrier protein of Brassica napus is encoded by a distinct, nuclear multigene family

Acyl-carrier protein (ACP) is a key component involved in the regulation of fatty acid biosynthesis in plants. cDNA clones encoding ACP from Brassica napus (oil seed rape) embryos have been isolated using oligonucleotide probes derived from heterologous ACPs. Analysis of the DNA sequence data, in conjunction with N-terminal amino acid sequence data, revealed ACP to be synthesized from nuclear DNA as a precursor containing a 51-amino-acid N-terminal extension. Immunocytochemical studies showed ACP to be localised solely within the plastids of B. napus seed tissue and it would therefore appear that the N-terminal extension functions as a transit peptide to direct ACP into these organelles. Analysis of several cDNA clones revealed sequence heterogeneity and thus evidence for an ACP multigene family. From ten cDNA clones, six unique genes, encoding five different mature ACP polypeptides, were identified. Northern blot hybridisation studies provide evidence that the seed and leaf forms of rape ACP are encoded by structurally distinct gene sets.

Neurospora mitochondria contain an acyl-carrier protein

Mitochondria of Neurospora crassa were found to contain a protein which was labelled with [14C]pantothenic acid and which carried an acyl group. This protein, when purified 6000-fold, closely resembled the bacterial and chloroplast acyl-carrier protein(s) [ACP(s)] in its physical and chemical properties. The predominant acyl group esterified to the purified protein was 3-hydroxytetradecanoate, as determined by gas chromatographic mass spectrometry. The amino acid sequence of the tryptic peptide carrying the 4'-phosphophantetheine moiety showed a high degree of sequence similarity to the analogous bacterial and chloroplast ACP peptide sequences. The possible functions of this ACP in lipid metabolism are discussed in view of the fact that Neurospora has a separate cytoplasmic enzyme complex which carries out the de novo biosynthesis of fatty acids.

Synthesis, cloning, and expression in Escherichia coli of a spinach acyl carrier protein-I gene

A synthetic gene of 268 bp encoding the 82 amino acid spinach acyl carrier protein (ACP)-I was constructed based on the known amino acid sequence. Two gene fragments, one encoding the amino-terminal portion and the other the carboxy-terminal portion of the protein, were assembled from synthetic oligonucleotides and inserted into the phage M13mp19. These partial gene constructions were joined and inserted into the plasmid pTZ19R. DNA sequencing confirmed the accuracy of the constructions. The synthetic gene was then subcloned into the Escherichia coli expression vector pKK233-2, under the control of the trc promoter. Western blot analysis and radioimmunoassay indicated that E. coli cells carrying this plasmid produced up to 6 mg/liter of a protein which was immunologically cross-reactive and similar in electrophoretic mobility to authentic spinach acyl carrier protein. The bacterial cells were able to attach the phosphopantetheine prosthetic group to the synthetic plant gene product allowing it to be acylated in vitro by acyl-ACP synthetase.

Molecular cloning and sequencing of a cDNA encoding the acyl carrier protein and its flanking domains in the mammalian fatty acid synthetase

Cloned cDNAs containing coding sequences for domains proximal to the carboxy terminus of the rat fatty acid synthetase have been isolated using an expression vector and domain-specific antibodies. The coding regions were assigned to specific domains of the multifunctional complex by identification of sequences coding for characterized peptide fragments and by recognition of sequences homologous to other monofunctional enzymes. Two clones contain the entire coding region for the acyl carrier protein domain. The sequence is flanked at the 3'-end by a region coding for the thioesterase domain and at the 5'-end by a sequence coding for a reductase, most likely the ketoreductase domain. Thus the ordering of these domain-coding regions in the fatty acid synthetase mRNA is established. The acyl carrier protein domain exhibits about 25% homology with that of the discrete monofunctional acyl carrier proteins of Escherichia coli, spinach and barley, the ketoreductase domain exhibits about 25% homology with bacterial dihydrofolate reductases and the active site of the thioesterase domain exhibits both primary and secondary structural features common to the serine proteases. These findings lend support to the hypothesis that the polyfunctional fatty acid synthetase probably arose by a complex evolutionary process involving fusion of genes coding for seven individual enzymes.

The amphiphilicity of ACP helices: a means of macromolecular interaction?

ACP interacts with diverse proteins in an unknown way. Possibly there is a similar mode of interaction between ACP and all ACP-binding proteins, the amphiphilic helix. The hydrophobicities of helices from 4 different ACPs were compared. Hydrophobic moment plots were prepared for ACP helices and those of many EF hand calcium-binding proteins. Both groups of proteins occupied the same region of the plot.

Isolation of a cDNA clone for the acyl carrier protein-I of spinach

A 715 base pair cDNA clone coding for an acyl carrier protein (ACP) in spinach leaves has been isolated and characterized. The amino acid sequence indicated by the cDNA sequence closely matches the amino acid sequence of the ACP-I isoform. The presence of polyadenylation and DNA sequence coding for a precursor protein with a putative transit peptide, and the absence of hybridization between the cloned DNA and isolated spinach plastid DNA collectively show that the ACP-I gene is nuclear-encoded. The ACP-I cloned DNA did not cross-hybridize with mRNA from spinach tissues in which ACP-II has been found. Cross-hybridization with mRNA from tissues of Brassica campestris was either weak or undetectable. The cloning of an ACP-I gene represents an initial step in the molecular dissection of fatty acid synthetase in plants.