Structure and DNA sequence of the tropomyosin I gene from Drosophila melanogaster

From action potential to contraction: neural control and excitation-contraction coupling in larval muscles of Drosophila

The neuromuscular system of Drosophila melanogaster has been studied for many years for its relative simplicity and because of the genetic and molecular versatilities. Three main types of striated muscles are present in this dipteran: fibrillar muscles, tubular muscles and supercontractile muscles. The visceral muscles in adult flies and the body wall segmental muscles in embryos and larvae belong to the group of supercontractile muscles. Larval body wall muscles have been the object of detailed studies as a model for neuromuscular junction function but have received much less attention with respect to their mechanical properties and to the control of contraction. In this review we wish to assess available information on the physiology of the Drosophila larval muscular system. Our aim is to establish whether this system has the requisites to be considered a good model in which to perform a functional characterization of Drosophila genes, with a known muscular expression, as well as Drosophila homologs of human genes, the dysfunction of which, is known to be associated with human hereditary muscle pathologies.

Analysis of tarantula skeletal muscle protein sequences and identification of transcriptional isoforms

Background

Tarantula has been used as a model system for studying skeletal muscle structure and function, yet data on the genes expressed in tarantula muscle are lacking.

Results

We constructed a cDNA library from Aphonopelma sp. (Tarantula) skeletal muscle and got 2507 high-quality 5'ESTs (expressed sequence tags) from randomly picked clones. EST analysis showed 305 unigenes, among which 81 had more than 2 ESTs. Twenty abundant unigenes had matches to skeletal muscle-related genes including actin, myosin, tropomyosin, troponin-I, T and C, paramyosin, muscle LIM protein, muscle protein 20, a-actinin and tandem Ig/Fn motifs (found in giant sarcomere-related proteins). Matches to myosin light chain kinase and calponin were also identified. These results support the existence of both actin-linked and myosin-linked regulation in tarantula skeletal muscle.

We have predicted full-length as well as partial cDNA sequences both experimentally and computationally for myosin heavy and light chains, actin, tropomyosin, and troponin-I, T and C, and have deduced the putative peptides. A preliminary analysis of the structural and functional properties was also carried out. Sequence similarities suggested multiple isoforms of most myofibrillar proteins, supporting the generality of multiple isoforms known from previous muscle sequence studies. This may be related to a mix of muscle fiber types.

Conclusion

The present study serves as a basis for defining the transcriptome of tarantula skeletal muscle, for future in vitro expression of tarantula proteins, and for interpreting structural and functional observations in this model species.

Echinococcus granulosus tropomyosin isoforms: from gene structure to expression analysis

Tropomyosins (Trps) constitute a family of actin filament-binding proteins found in all eukaryotic cells. In muscle cells, they play a central role in contraction by regulating calcium-sensitive interaction of actin and myosin. In non-muscle cells, tropomyosins regulate actin filament organization and dynamics. Trps genes exhibit extensive cell type-specific isoform diversity generated by alternative splicing. Here, we report the characterization of tropomyosin gene transcribed sequences from the parasitic platyhelminth Echinococcus granulosus. Using RT-PCR approach we isolated three isoforms (egtrpA, egtrpB and egtrpC), which display significant homologies to know tropomyosins of different phylogenetic origin. The corresponding gene, egtrp (5656 bp), contains eight introns and nine exons. Southern blot hybridization studies showed that egtrp is present as single copy locus in E. granulosus. We demonstrated that egtrp expresses three different transcripts which differ in alternatively spliced exon 4 and intron VI. Interestingly, intron VI suffers intron retention and contains an internal stop codon in frame. Three major bands are also detected by Western blot analysis using a specific anti-rEgTrp antiserum. Immune-localization and in situ hybridization studies showed that egtrp transcription and translation is mostly localized at the protoscoleces suckers. This is the first report of alternative splicing in this parasite.

A genetic modifier screen identifies multiple genes that interact with Drosophila Rap/Fzr and suggests novel cellular roles

In the developing Drosophila eye, Rap/Fzr plays a critical role in neural patterning by regulating the timely exit of precursor cells. Rap/Fzr (Retina aberrant in pattern/Fizzy related) is an activator of the E3 Ubiquitin ligase, the APC (Anaphase Promoting Complex-cyclosome) that facilitates the stage specific proteolytic destruction of mitotic regulators, such as cyclins and cyclin-dependent kinases. To identify novel functional roles of Rap/Fzr, we conducted an F(1) genetic modifier screen to identify genes which interact with the partial-loss-function mutations in rap/fzr. We screened 2741 single P-element, lethal insertion lines and piggyBac lines on the second and third chromosome for dominant enhancers and suppressors of the rough eye phenotype of rap/fzr. From this screen, we have identified 40 genes that exhibit dosage-sensitive interactions with rap/fzr; of these, 31 have previously characterized cellular functions. Seven of the modifiers identified in this study are regulators of cell cycle progression with previously known interactions with rap/fzr. Among the remaining modifiers, 27 encode proteins involved in other cellular functions not directly related to cell-cycle progression. The newly identified variants fall into at least three groups based on their previously known cellular functions: transcriptional regulation, regulated proteolysis, and signal transduction. These results suggest that, in addition to cell cycle regulation, rap/fzr regulates ubiquitin-ligase-mediated protein degradation in the developing nervous system as well as in other tissues.

Tropomyosin-based regulation of the actin cytoskeleton in time and space

Tropomyosins are rodlike coiled coil dimers that form continuous polymers along the major groove of most actin filaments. In striated muscle, tropomyosin regulates the actin-myosin interaction and, hence, contraction of muscle. Tropomyosin also contributes to most, if not all, functions of the actin cytoskeleton, and its role is essential for the viability of a wide range of organisms. The ability of tropomyosin to contribute to the many functions of the actin cytoskeleton is related to the temporal and spatial regulation of expression of tropomyosin isoforms. Qualitative and quantitative changes in tropomyosin isoform expression accompany morphogenesis in a range of cell types. The isoforms are segregated to different intracellular pools of actin filaments and confer different properties to these filaments. Mutations in tropomyosins are directly involved in cardiac and skeletal muscle diseases. Alterations in tropomyosin expression directly contribute to the growth and spread of cancer. The functional specificity of tropomyosins is related to the collaborative interactions of the isoforms with different actin binding proteins such as cofilin, gelsolin, Arp 2/3, myosin, caldesmon, and tropomodulin. It is proposed that local changes in signaling activity may be sufficient to drive the assembly of isoform-specific complexes at different intracellular sites.

Transcriptional regulation of the Drosophila melanogaster muscle myosin heavy-chain gene

We show that a 2.6kb fragment of the muscle myosin heavy-chain gene (Mhc) of Drosophila melanogaster (containing 458 base pairs of upstream sequence, the first exon, the first intron and the beginning of the second exon) drives expression in all muscles. Comparison of the minimal promoter to Mhc genes of 10 Drosophila species identified putative regulatory elements in the upstream region and in the first intron. The first intron is required for expression in four small cells of the tergal depressor of the trochanter (jump) muscle and in the indirect flight muscle. The 3'-end of this intron is important for Mhc transcription in embryonic body wall muscle and contains AT-rich elements that are protected from DNase I digestion by nuclear proteins of Drosophila embryos. Sequences responsible for expression in embryonic, adult body wall and adult head muscles are present both within and outside the intron. Elements important for expression in leg muscles and in the large cells of the jump muscle flank the intron. We conclude that multiple transcriptional regulatory elements are responsible for Mhc expression in specific sets of Drosophila muscles.

Heterogeneity and tissue specificity of tropomyosin isoforms from four species of bivalves

Heterogeneity and tissue specificity of tropomyosin isoforms obtained from four species of bivalves (Scapharca broughtonii (ark shell), Mytilus galloprovincialis (mussel), Atrina pectinata (surf clam) and Crassostrea gigas (Pacific oyster)), were examined. Tropomyosins were extracted from translucent and opaque portions of posterior adductor muscle, respectively, and cardiac muscle of each bivalve. There were two tropomyosin isoforms in the ark shell, the surf clam and the Pacific oyster. They were designated as TMa and TMb. In the ark shell, TMa was the common isoform and TMb was specific for the opaque portion of the adductor muscle. In the surf clam, TMb was the common isoform present in all tissues. TMa was found only in the translucent portion of muscle. In the Pacific oyster, TMb was the major component in both portions of adductor muscle and TMa was the major component in cardiac muscle, although both tropomyosins were included in all tissues. The mussel had only one tropomyosin.

Invertebrate Muscles: Muscle Specific Genes and Proteins

This is the first of a projected series of canonic reviews covering all invertebrate muscle literature prior to 2005 and covers muscle genes and proteins except those involved in excitation-contraction coupling (e.g., the ryanodine receptor) and those forming ligand- and voltage-dependent channels. Two themes are of primary importance. The first is the evolutionary antiquity of muscle proteins. Actin, myosin, and tropomyosin (at least, the presence of other muscle proteins in these organisms has not been examined) exist in muscle-like cells in Radiata, and almost all muscle proteins are present across Bilateria, implying that the first Bilaterian had a complete, or near-complete, complement of present-day muscle proteins. The second is the extraordinary diversity of protein isoforms and genetic mechanisms for producing them. This rich diversity suggests that studying invertebrate muscle proteins and genes can be usefully applied to resolve phylogenetic relationships and to understand protein assembly coevolution. Fully achieving these goals, however, will require examination of a much broader range of species than has been heretofore performed.

Tropomyosin isoforms present in the sea anemone, Anthopleura japonica (Anthozoa, Cnidaria)

Five isoforms of tropomyosin, designated as TMa, TMb, TMc, TMd, and TMe, were detected in the sea anemone, Anthopleura japonica. The apparent molecular weights of these isoforms were estimated to be approximately 30 kD to 37.5 kD, and their pI values were approximately 4.55 (TMa and TMb) and 4.65 (TMc, TMd, and TMe). Although sea anemone tropomyosin isoforms have the ability to bind to rabbit skeletal muscle actin, they preferably bind to actin at higher concentrations of Mg(2+) (10-20 mM) and slightly lower pH (6.2-7.2) than those used in conventional conditions. Antigenic properties of sea anemone tropomyosin seemed to be considerably specific to each isoform. Distribution of tropomyosin isoforms in the sea anemone body was somewhat portion-specific. TMa, TMb, and TMe were detected similarly in the extracts from tentacle, oral disc, column, mouth, and pedal disc. Although TMc and TMd were detected abundantly in the tentacle extract and moderately in the column and mouth extracts, these components were not contained in the pedal disc extract and detected only faintly in the oral disc extract.

A tropomyosin-2 mutation suppresses a troponin I myopathy in Drosophila

A suppressor mutation, D53, of the held-up(2) allele of the Drosophila melanogaster Troponin I (wupA) gene is described. D53, a missense mutation, S185F, of the tropomyosin-2, Tm2, gene fully suppresses all the phenotypic effects of held-up(2), including the destructive hypercontraction of the indirect flight muscles (IFMs), a lack of jumping, the progressive myopathy of the walking muscles, and reductions in larval crawling and feeding behavior. The suppressor restores normal function of the IFMs, but flight ability decreases with age and correlates with an unusual, progressive structural collapse of the myofibrillar lattice starting at the center. The S185F substitution in Tm2 is close to a troponin T binding site on tropomyosin. Models to explain suppression by D53, derived from current knowledge of the vertebrate troponin-tropomyosin complex structure and functions, are discussed. The effects of S185F are compared with those of two mutations in residues 175 and 180 of human alpha-tropomyosin 1 which cause familial hypertrophic cardiomyopathy (HCM).

Ectopic expression of MEF2 in the epidermis induces epidermal expression of muscle genes and abnormal muscle development in Drosophila

Myocyte-specific enhancer-binding factor 2 (MEF2) is a myogenic regulatory factor in vertebrates and Drosophila. Whereas the role of MEF2 in regulating vertebrate myogenesis and muscle genes has been extensively studied, little is known of the role of MEF2 in regulating Drosophila myogenesis. We have shown in a recent analysis of the regulation of the Drosophila Tropomyosin I (TmI) gene in transgenic flies that MEF2 is a positive regulator of TmI expression in the somatic body-wall muscles of embryos, larvae, and adults. To understand further the role of MEF2 in myogenesis and test the role of MEF2 in regulating TmI expression, we have used the yeast GAL4/UAS system to generate embryos in which MEF2 is ectopically expressed in tissues where it is not normally expressed or embryos in which MEF2 is overexpressed in the mesoderm and muscles. We observe that ectopic expression of MEF2 in the epidermis and the ventral midline cells in embryos activates the expression of TmI and other muscle genes in these tissues and that this activation is stage-dependent suggesting a requirement for additional factors. Furthermore, ectopic expression of MEF2 in the epidermis results in a decrease in the expression of signaling molecules in the epidermis and a failure of the embryo to properly form body-wall muscles. These results indicate that MEF2 can function out of context in the epidermis to induce the expression of muscle genes and interfere with a requirement for the epidermis in muscle development. We also find that the level of MEF2 in the mesoderm and/or muscles in embryos is critical to body-wall muscle formation; however, no effect is observed on the development of the visceral muscle or dorsal vessel.

Characterisation of fast, slow and cardiac muscle tropomyosins from salmonid fish

Tropomyosin (TM) has been isolated from the cardiac muscle, and fast and slow trunk (myotomal) muscles of the mature salmonid fish Atlantic salmon (Salmo salar) and rainbow trout (Salmo gairdneri). When examined electrophoretically, isoforms of TM were detected which were specific, and exclusive, to each type of muscle. Cardiac and fast muscles contained single and distinct isoforms, while slow muscle contained two distinct isoforms, closely related in terms of apparent M(r), and pI. There was no detectable difference between the same TM type from either salmon or trout. On a variety of gel systems, the cardiac and slow isoforms migrated in close proximity to each other and to rabbit alpha-TM. The fast isoform comigrated with rabbit beta-TM. In developing salmon fry, a more acidic (unphosphorylated) variant of TM was present in addition to, and of similar M(r) to, the fast adult isoform. This TM declined in steady-state level during maturation and was virtually undetected in adult muscle. All of the isolated TMs contained little or no covalently bound phosphate and were blocked at the N-terminus. The amino acids released by carboxypeptidase A, when ordered to give maximal similarity to other muscle TMs, were consistent with the following sequences: fast (LDNALNDMTSI) and cardiac (LDHALNDMTSL). The C-terminal region of the slow TM contained His but was heterogeneous. In viscosity measurements, performed as a function of increasing protein concentration, at low ionic strength (t = 5 degrees C, pH 7.00), fast TM exhibited the highest relative viscosity values. Lower and equivalent levels of polymerisation occurred with the cardiac and slow TMs. Polymerisation of all three isoforms was temperature-dependent, with cardiac TM being least sensitive and fast TM being most sensitive. Determination of the complete coding sequence of adult fast TM confirmed the findings of the carboxypeptidase analysis, but the remainder of the sequence more closely resembled alpha-type TMs than beta-type TMs. Overall, salmon fast TM contains 20 (mostly conservative) substitutions compared to rabbit striated muscle alpha-TM and 40 (mostly conservative) substitutions compared to rabbit striated muscle beta-TM. This demonstrates that electrophoretic mobility is not, in all instances, a suitable method to assess the isomorphic nature of striated muscle TMs.

Interspecific sequence comparison of the muscle-myosin heavy-chain genes from Drosophila hydei and Drosophila melanogaster

The muscle-myosin heavy-chain (mMHC) gene of Drosophila hydei has been sequenced completely (size 23.3 kb). The sequence comparison with the D. melanogaster mMHC gene revealed that the exon-intron pattern is identical. The protein coding regions show a high degree of conservation (97%). The alternatively spliced exons (3a-b, 7a-d, 9a-c, 11a-e, and 15a-b) display more variations in the number of nonsynonymous and synonymous substitutions than the common exons (2, 4, 5, 6, 8, 10, 12, 13, 14, 16, 17, and 19). The base composition at synonymous sites of fourfold degenerate codons (third position) is not biased in the alternative exons. In the common exons there exists a bias for C and against A. These findings imply that the alternative exons of the Drosophila mMHC gene evolve at a different, in several cases higher, rate than the common ones. The 5' splice junctions and 5' and 3' untranslated regions show a high level of similarity, indicating a functional constraint on these sequences. The intron regions vary considerably in length within one species, but the corresponding introns are very similar in length between the two species and all contain stretches of sequence similarity. A particular example is the first intron, which contains multiple regions of similarity. In the conserved regions of intron 12 (head-tail border) sequences were found which have the potential to direct another smaller mMHC transcript.

Clonorchis sinensis tropomyosin: cloning and sequence of partial cDNA amplified by PCR

C. sinensis total RNA was containing large amount of 18S rRNA but little 28S rRNA. The size of the double-stranded cDNA synthesized from poly (A)+ mRNA was 0.4-4.2 kb long with tapering upto 9.5 kb. Degenerated oligonucleotides (as 2 sense and 3 antisense primers) were designed on the conserved regions of the known tropomyosin amino acid sequences. From one out of the PCR amplifications using total cDNA and matrix of primers, a specific gene product, 580 bp in size, was produced. Upon Southern hybridization of the PCR products with Schistosoma mansoni tropomyosin (SMTM) cDNA, only one signal appeared at the band of 580 bp product. This 580 bp product was considered to encode C. sinensis tropomyosin (CSTM) and cloned in pGEM-3Zf(-) for DNA sequencing. CSTM cDNA was 575 bp containing one open reading frame of 191 predicted amino acids, which revealed 86.3% homology with SMTM and 51.1% with Trichostrongylus colubriformis tropomyosin. CSTM cDNA obtained will serve as a probe in the studies of molecular cloning of CSTM.

Characterization of a tropomyosin cDNA from the hydrozoan Podocoryne carnea

A cDNA clone from the hydrozoan Podocoryne carnea was characterized. It consists of an open reading frame of 726 nt flanked by a 84 nt 5' and a 307 nt 3' untranslated region. The corresponding gene exists apparently as a single copy. The transcript is ubiquitously expressed in the polyp and the medusa stage. Several features of the predicted peptide sequence indicate a relationship to tropomyosins. At the amino acid level it shares 26-30% identical residues with other invertebrate and vertebrate tropomyosin sequences.

Isolation, purification and partial characterization of tropomyosin and troponin subunits from the lobster tail muscle

In a search for an invertebrate muscle from which the muscle regulatory proteins could be obtained in a great quantity and at high homogeneity, the regulatory proteins, tropomyosin (Tm) and three subunits of troponin (Tn), have been isolated from the lobster tail muscle, purified and partially characterized. The calcium-sensitive ATPase of lobster myofibril was restored when purified lobster Tm and lobster Tn were added to actin. Quantitative SDS-polyacrylamide gel electrophoresis showed that the lobster muscle contains actin, Tm, Tn with a molar ratio 7:1:1 and that lobster Tn consists of three subunits, one of each I, C and T. Each subunit was identified according to its effect on the acto-S1 ATPase rate. The isomer composition in each fraction of purified Tn subunit and in Tm are different from the rabbit skeletal muscle proteins; Tm consists of a single species of polypeptide of M(r) 38,000; the TnT fraction appears to be homogeneous with M(r) 43,000; the TnI fraction contains five isomers, all showing similar isoelectric pH, differing in M(r) in the range from 28,000 to 31,000; two TnC fractions contain three isomers in total with a range of M(r) from 18,500 to 19,000. Further study of the lobster Tm elucidated that digestion by carboxypeptidase A gave rise to a homogeneous preparation of truncated and non-polymerizable Tm which is devoid of 11 residues at the C-terminus of the molecule. The C-terminal amino acid sequence of 11 residues is homologous to the thoracic isomer generated from Drosophila melanogaster Tm-I gene. The present study indicated that, despite heterogeneities owing to the occurrence of isomers, the lobster regulatory proteins serve as an invertebrate source of the proteins for structural and biophysical studies, alternative to vertebrate counterparts.

In vitro transcription analysis of the Drosophila tropomyosin and other muscle genes

Nuclear transcription extracts were prepared from embryos of Drosophila melanogaster to study the in vitro transcription of the tropomyosin genes. Several non-muscle gene promoters, including the non-muscle promoter of the Tropomyosin II gene, were shown to be efficiently transcribed in vitro. The Tropomyosin I gene and the muscle promoter of the Tropomyosin II gene, as well as two other contractile protein muscle genes, were not transcribed in vitro. The embryonic extract did, however, contain developmental-specific proteins that bound to the muscle enhancer regulatory region of the Tropomyosin I gene.

Structural homology of tropomyosins from the human trematode Schistosoma mansoni and its intermediate host Biomphalaria glabrata

Molecular mimicry has been considered as a possible way for parasites to escape host immune responses. This work concerns the characterization of protein determinants shared by Schistosoma mansoni and its intermediate host Biomphalaria glabrata. Parasite (Sm39) and mollusc (Bg 39) cross-reactive proteins were identified and shown to induce in rabbit and mouse, antibodies specific for invertebrate determinants. Ultrastructural studies demonstrated that antibodies to Sm39 specifically bound to muscular structures of parasite and mollusc. Molecular cloning and sequencing indicated that Bg39 corresponded to a muscular isoform of tropomyosin. The mollusc sequence showed a 51-65% homology with seven different muscular tropomyosins from vertebrate and invertebrate species. The highest score of homology was observed with S. mansoni tropomyosin, suggesting that cross-reactive determinants could be specific for the trematode and its intermediate host. In miracidia, Sm39 epitopes were also shown to be contained in the vesicles present in epidermal ridges and cellular bodies. Such vesicles are involved in the formation of a protective tegument around sporocysts, suggesting a possible role of cross-reactive tropomyosins in miracidia and/or sporocyst-snail interactions.

Tropomyosin has discrete actin-binding sites with sevenfold and fourteenfold periodicities

Analysis of the periodic distribution of amino acids in tropomyosin has revealed the presence of seven or 14 quasi-equivalent actin-binding sites. We tested the hypothesis of periodic actin-binding sites by making deletions of chicken striated alpha-tropomyosin cDNA using oligonucleotide-directed mutagenesis. The deletions corresponded to one-half (amino acid residues 47 to 67), two-thirds (residues 47 to 74) and one actin-binding site (residues 47 to 88), on the basis of there being seven sites. The mutant cDNAs were expressed as fusion and non-fusion proteins in Escherichia coli and analyzed for actin binding and regulatory function. Fusion tropomyosin binds to actin with an affinity similar to that of muscle tropomyosin. Of the mutant fusion tropomyosins, only that with a full site deleted retained actin affinity and the ability to inhibit the actomyosin S1 ATPase, though it was less effective than wild-type. We conclude that an integral number of half-turns of the tropomyosin coiled-coil, and the consequential sevenfold periodicity, as well as the correct orientation of the ends with respect to each other, are important for actin binding. On the other hand, non-fusion tropomyosin binds well to actin only in the presence of troponin, and the binding is calcium-sensitive. Assay of non-fusion mutant tropomyosins showed that mutants with deletion of one-half and one actin binding site both had high affinity for actin, equal to or slightly less than wild-type. The ability of these two mutants to regulate the actomyosin or acto-S1 ATPase with troponin in the absence of calcium was indistinguishable from that of the wild-type. The normal regulatory function of the mutant with a 1/14 deletion (removal of a quarter turn or half a site) indicates that a 14-fold periodicity is adequate for regulation, consistent with the presence of two sets of seven alpha and seven beta quasi-equivalent actin-binding sites. An alternative explanation is that the alpha-sites are of primary importance and that proper alignment of the alpha-sites in every second tropomyosin, as when half a site is deleted, is sufficient for normal regulatory function. Deletion of a non-integral period (2/3 of a site) severely compromised actin-binding and regulatory function, presumably due to the inability of the mutant to align properly on the actin filament.

Characterization of cDNA clones coding for muscle tropomyosin of the nematode Trichostrongylus colubriformis

The host-protective antigen from detergent-solubilised extracts of the sheep intestinal helminth Trichostrongylus colubriformis has been identified as tropomyosin. Complementary DNA clones coding for T. colubriformis muscle tropomyosin have been isolated and characterised as the first step in obtaining recombinant protein to carry out more extensive vaccination trials. The clones represent an mRNA of 1544 bases, including a relatively long 5' untranslated sequence of 307 bases and a 3' non-coding region of 344 bases. The mRNA codes for a highly alpha-helical protein of 284 residues with a molecular weight of 33,000; characteristics typically observed for the muscle tropomyosins of higher organisms. The T. colubriformis protein has 58% sequence identity with rabbit and Drosophila melanogaster muscle tropomyosins, and the differences in the protein sequence are randomly distributed throughout the molecule. There is complete identity between the three sequences for the N-terminal 9 residues, the region believed to be essential for the polymerisation of tropomyosin molecules and for binding to actin and troponin.

Schistosoma mansoni tropomyosin: cDNA characterization, sequence, expression, and gene product localization

We have defined the polypeptide pattern of 3-hr Schistosoma mansoni schistosomula on nonequilibrium two-dimensional gels (NEPHGE). An acidic group of polypeptides with a molecular weight of about 40 kDa and a pI value of around 5.0 (numbered 48/59/53) were identified as antigens on Western blots probed with chronic human infection sera or vaccinated mouse sera. Polypeptides 48/49/53 from silver-stained NEPHGE gels produced antisera that were specific as demonstrated by Western blot analysis and immunoprecipitations of in vitro translation products. A cDNA clone (clone 1) from a S. mansoni adult worm pBR322 library was isolated by using cDNA probes made from size-fractionated mRNA and defined as encoding polypeptide 49 by hybridization selection of the mRNA which was in vitro translated and immunoprecipitated with specific mouse antiserum. A lambda gt 11 expression clone which contained an insert close to the full length mRNA was isolated from a S. mansoni cercariae library. The complete sequence of the mRNA was determined by sequencing the insert of this clone as well as primer extension of total RNA. The only open reading frame coding for 284 amino acids in the 1316 nucleotide sequence showed a 44.76 to 55.44% homology with the amino acid sequences of 18 different tropomyosins from various species. Computer-predicted secondary structure of schistosome tropomyosin was mainly alpha-helix which was very similar to other tropomyosins. Northern analysis showed the mRNA to be about 1.5 kb in size and detectable at much higher levels in the adult worm stage as compared to the cercariae and the egg stages. Western blot analysis likewise showed that greater amounts of tropomyosin were detected in extracts from adult worm stage as compared to extracts from cercariae and egg stages. Immunocytochemical analysis shows that tropomyosin is strongly associated with the tegument of adult worms. The restriction digestion pattern given by genomic Southern analysis suggests the existence of introns and/or multiple gene copies. Thus polypeptide 49, an immunodominant antigen, represents schistosome tropomyosin.

An actin-interacting heptapeptide in the cofilin sequence

Cofilin, a 21-kDa actin-binding protein, has a hexapeptide sequence DAIKKK which is identical to the N-terminal portion (residues 2-7) of tropomyosin. The synthetic heptapeptide, DAIKKKL, corresponding to residues 122-128 of cofilin, inhibited the binding of cofilin to F-actin in a dose-dependent manner. The heptapeptide cosedimented with F-actin, decreased the fluorescence intensity of pyrene-labeled F-actin, and increased the rate of polymerization of G-actin. The hexapeptides, DIKKKL and DAIKKL, also inhibited the binding of cofilin to F-actin and affected the fluorescence intensity of pyrene-labeled F-actin and the rate of actin polymerization, like the heptapeptide. However, their effects were weaker than those of the heptapeptide. Moreover, the pentapeptide, DIKKL, had little or no effect. These results suggest that the heptapeptide sequence is specific for the interaction with actin and, therefore, may constitute part of the actin-binding domain of cofilin.

The Drosophila ets-2 gene: molecular structure, chromosomal localization, and developmental expression

The cellular homologs of the ets gene from the avian erythroblastosis retrovirus E26 have been studied in chickens, humans, mice, and cats. In this report a further evolutionary step is taken by isolating and characterizing a Drosophila ets-related genomic clone. Sequence analysis of this clone has shown it to contain the 3' end of the v-ets gene, called ets-2, corresponding to the last two exons of chicken ets. The predicted amino acid sequence was found to have over 90% homology when compared to that of v-ets. This is the highest level of conservation observed for any previously characterized Drosophila oncogene homolog. Expression of the ets-2 gene occurs throughout development, but is highest during the embryonic and pupal stages. By in situ hybridization, the ets-2 chromosomal position was determined to be 58A/B which corresponds to no known phenotypic mutant. As this is a highly conserved gene, the Drosophila model system should prove useful for the determination of the ets gene function.

Fluorescence of equine platelet tropomyosin labeled with acrylodan

Equine platelet tropomyosin was labeled with the sulfhydryl-specific fluorescent reagent 6-acryloyl-2-dimethylaminonaphthalene (acrylodan). The extent of labeling at 4 degrees C could be regulated between 0.5 and 1.3 acrylodans per tropomyosin chain by varying the reaction time from 1 to 4.5 h. Acrylodan-labeled platelet tropomyosin, AD-P-TM, was highly fluorescent, having an emission maximum near 518 nm on excitation at 365 nm. Steady-state measurements of polarization of the fluorescence of AD-P-TM in both low and high ionic strength solutions gave Perrin plots that exhibited sharp changes in slope near 50 degrees C, indicative of a sharp increase in mobility of the label at that temperature. This correlates with the melting temperature of the platelet tropomyosin coiled coil observed by circular dichroism [G. P. Côté, W. G. Lewis, M. D. Pato, and L. B. Smillie, (1978) FEBS Lett. 91, 237-241]. Perrin plots of carboxypeptidase A-treated platelet tropomyosin that was labeled with acrylodan after digestion resembled more closely those of acrylodan-labeled cardiac tropomyosin rather than those of AD-P-TM, suggesting that the observed emission arose from label at Cys-153 on each truncated platelet tropomyosin chain. In solutions containing 150 mM KCl and 5 mM MgCl2, addition of actin at up to a sixfold molar excess over AD-P-TM caused both the fluorescence emission intensities and fluorescence polarization values of samples to increase. In the presence of actin, the wavelength of maximal emission was shifted to shorter values by about 5 to 7 nm. These changes indicate that actin does bind to AD-P-TM and that the binding affects the environment of the label, both by making it more hydrophobic and by reducing the freedom of the label to tumble in solution.

Rat glycine methyltransferase. Complete amino acid sequence deduced from a cDNA clone and characterization of the genomic DNA

The amino terminus of glycine methyltransferase from rat liver is blocked. A hexapeptide containing the blocked amino-terminal residue was obtained from a tryptic digest of the purified enzyme and its amino acid sequence was determined to be Ac-Val-Asp-Ser-Val-Tyr-Arg by Edman degradation and fast-atom-bombardment mass spectrometry after fragmentation with Staphylococcus aureus protease V8. A full-length cDNA clone for the enzyme was isolated from a lambda gt11 rat liver cDNA library using the previously obtained pGMT A56 cDNA [Ogawa, H., Gomi, T., Horii, T., Ogawa, H. & Fujioka, M. (1984) Biochem. Biophys. Res. Commun. 124, 44-50] as a probe. The amino acid sequence deduced from the nucleotide sequence contained both amino- and carboxyl-terminal sequences. The predicted amino acid composition and molecular mass were also in agreement with the published data obtained with the purified protein. Five clones for the glycine methyltransferase gene were isolated from a Charon 4A library containing EcoRI digest of rat liver DNA by in situ plaque hybridization. All clones had inserts of 6500 base pairs, consistent with the size of EcoRI genomic DNA fragment determined by Southern blot hybridization. Sequence analysis of a 5400-bp fragment of the insert DNA lacking a 1100-bp 5' region and comparison of the sequence with that of the cDNA showed that the insert DNA entirely encoded glycine methyltransferase and the gene consisted of six exons and five introns. S1 nuclease protection mapping and primer extension analysis allowed us to propose that the A residue located 19 bp upstream from the translation initiation codon is the site of transcription initiation. TATA, CAAT and GC sequences, and the complementary sequence to the enhancer core element, were located upstream of the transcription initiation site.

Structure and sequence of the Drosophila melanogaster calmodulin gene

A series of phage clones overlapping the single calmodulin gene locus of Drosophila melanogaster has been isolated and the exons of the gene positioned and sequenced within these clones. A calmodulin cDNA clone of the electric eel was used to identify these clones and to position the two major protein-coding exons of the gene. cDNA clones for D. melanogaster calmodulin were then isolated, characterized and used to identify the remaining exons. The gene consists of four exons separated by three introns of 3400 to 4300 bases in length. Exon 1 consists of the 5' untranslated region and the initiator ATG; exon 2 encodes amino acid residues 1 to 58.3; exon 3 encodes residues 58.3 to 139.3; and exon 4 encodes residues 139.3 to 148 and the 3' untranslated region. From the sequence of the 3' untranslated region and the lengths of the cDNA clones, two or three polyadenylation sites are indicated. Sequences potentially involved in the control of transcription of the gene and splicing of the mRNA product have been identified. Comparison of the intron-exon structures of the D. melanogaster calmodulin gene, the chick calmodulin gene, and other genes of the troponin C superfamily reinforces previous hypotheses that these genes arose from a common progenitor and permits identification of four introns that were probably present in the progenitor gene structure. The D. melanogaster calmodulin gene contains three of these introns, and the chick gene contains all four. These gene comparisons also indicate that the region of these genes encoding Ca2+-binding loop 3 is highly variable in structure. The chick and D. melanogaster calmodulin genes differ in this region, the chick gene containing a fifth intron here that is absent from the D. melanogaster gene.

Nucleotide sequence of a cDNA clone encoding a Drosophila muscle tropomyosin II isoform

A cDNA clone was sequenced that contains the entire coding region for the muscle tropomyosin II isoform from Drosophila. The cDNA clone is 1253 nucleotides (nt) long and contains an 88-nt 5'-leader sequence and a 310-nt 3'-untranslated sequence. The muscle tropomyosin II isoform consists of 285 amino acids and is 60% homologous with the previously reported muscle tropomyosin I isoform Drosophila and 55% homologous with rabbit muscle tropomyosin.