Isolation and characterization of cDNA clones for human skeletal muscle alpha actin

Taurine chloramine-induced inactivation of cofilin protein through methionine oxidation

Cofilin regulates reorganization of actin filaments (F-actin) in eukaryotes. A recent finding has demonstrated that oxidation of cofilin by taurine chloramine (TnCl), a physiological oxidant derived from neutrophils, causes cofilin to translocate to the mitochondria inducing apoptosis (F. Klamt et al. Nat. Cell Biol.11:1241-1246; 2009). Here we investigated the effect of TnCl on biological activities of cofilin in vitro. Our data show that TnCl-induced oxidation of recombinant human cofilin-1 inhibits its F-actin-binding and depolymerization activities. Native cofilin contains four free Cys and three Met residues. Incubation of oxidized cofilin with DTT does not lead to its reactivation. A double Cys to Ala mutation on the two C-terminal Cys shows similar biological activities as the wild type, but does not prevent the TnCl-induced inactivation. In contrast, incubation of oxidized cofilin with methionine sulfoxide reductases results in its reactivation. Phosphorylation is known to inhibit cofilin activities. We found that Met oxidation also prevents phosphorylation of cofilin, which is reversed by incubating oxidized cofilin with methionine sulfoxide reductases. Interestingly, intact protein mass spectrometry of the oxidized mutant indicated one major oxidation product with an additional mass of 16 Da, consistent with oxidation of one specific Met residue. This residue was identified as Met-115 by peptide mapping and tandem mass spectrometry. It is adjacent to Lys-114, a known residue on globular-actin-binding site, implying that oxidation of Met-115 disrupts the globular-actin-binding site of cofilin, which causes TnCl-induced inactivation. The findings identify Met-115 as a redox switch on cofilin that regulates its biological activity.

BD SIMULATIONS OF THE IONIC STRENGTH DEPENDENCE OF THE INTERACTIONS BETWEEN TRIOSE PHOSPHATE ISOMERASE AND F-ACTIN

Functional protein-protein interactions are essential for many physiological processes. For example, the association of glycolytic enzymes to F-actin is proposed to be one mechanism through which glycolytic enzymes are compartmentalized, and as a result, play essential roles such as regulation of the glycolytic pathway and increasing glycolytic flux. Many glycolytic enzymes including fructose-1,6-bisphophate aldolase, glyceraldedhye-3-phosphate dehydrogenase, and lactate dehydrogenase bind F-actin strongly. Other glycolytic enzymes including triose phosphate isomerase (TPI) do not interact with F-actin significantly. Herein, Brownian dynamics (BD) simulations determine the energetics of the association of F-actin with the glycolytic enzyme triose phosphate isomerase as a function of ionic strength. This is the first thorough control study examining how well BD reproduces the experimental observations that the binding of TPI to F-actin is very weak and falls off rapidly as ionic strength increases. The BD results confirm experimental observations that the degree of association diminishes as ionic strength increases and that the interaction of TPI with F-actin is weakly nonspecific to nonexistent.

Spreading of antibody reactivity to non-thyroid antigens during experimental immunization with human thyroglobulin

Intermolecular spreading of antibody reactivity has been implicated in the evolution of autoimmune disease. In this study, spreading of antibody reactivity to non-thyroid autoantigens after experimental immunization with thyroglobulin (Tg) was investigated. For this purpose, two rabbits were injected with human Tg six times (stages 1-6) every 3 weeks. Animals were also bled before priming. Antisera were tested by enzyme-linked immunosorbent assay (ELISA) for reactivity to several non-thyroid antigens: bovine serum albumin (BSA), native DNA (nDNA), human myosin, human globular (G) and filamentous (F) actin and porcine tubulin. Tg-immunized animals developed the following serological reactivity pattern: (a) high reactivity to myosin from stage 2 onward, (b) significant reactivity to F-actin, remaining high up to stage 6, (c) reactivity to BSA with a peak at stage 3, (d) a small increase of reactivity to G-actin at stage 3 and (e) no increase of reactivity to nDNA and tubulin. The study of affinity-purified anti-Tg antibodies and the use of competitive assays revealed that reactivity to F-actin was not due to cross-reaction with Tg. On the contrary, reactivity to myosin during the first stages of immunization was due to cross-reaction with Tg, while at stage 6 it became myosin-specific. Reactivity to BSA at stage 3 was also due to cross-reaction with Tg. We conclude that at least part of the induced anti-Tg antibodies may result from the expansion of B cell clones producing polyreactive natural autoantibodies, and polyreactivity of anti-Tg antibodies during the first stages of Tg-immunization may be responsible for the intermolecular spreading of antibody response.

Molecular cloning and sequence of gilthead sea bream (Sparus aurata) alpha-skeletal actin: tissue and developmental expression

In the present study, the Sparus aurata alpha-skeletal actin was cloned from a mixed larvae complementary DNA library. The clone isolated was 1523 bp long with an open reading frame of 1134 bp coding for a 377-amino acid protein. The deduced amino acid sequence of sea bream alpha-actin is identical to Fugu alpha-actin-1. The expression of alpha-actin was initiated at the onset of segmentation. In adult fish, alpha-actin is expressed predominantly in white and red muscle.

Alternative splicing determines the intracellular localization of the novel nuclear protein Nop30 and its interaction with the splicing factor SRp30c

We report on the molecular cloning of a novel human cDNA by its interaction with the splicing factor SRp30c in a yeast two-hybrid screen. This cDNA is predominantly expressed in muscle and encodes a protein that is present in the nucleoplasm and concentrated in nucleoli. It was therefore termed Nop30 (nucleolar protein of 30 kDa). We have also identified a related cDNA with a different carboxyl terminus. Sequencing of the NOP gene demonstrated that both cDNAs are generated by alternative 5' splice site usage from a single gene that consists of four exons, spans at least 1800 nucleotides, and is located on chromosome 16q21-q23. The alternative 5' splice site usage introduces a frameshift creating two different carboxyl termini. The carboxyl terminus of Nop30 is rich in serines and arginines and has been found to target the protein into the nucleus, whereas its isoform is characterized by proline/glutamic acid dipeptides in its carboxyl terminus and is predominantly found in the cytosol. Interaction studies in yeast, in vitro protein interaction assays, and co-immunoprecipitations demonstrated that Nop30 multimerizes and binds to the RS domain of SRp30c but not to other splicing factors tested. Overexpression of Nop30 changes alternative exon usage in preprotachykinin and SRp20 reporter genes, suggesting that Nop30 influences alternative splice site selection in vivo.

Specific immunohistochemical detection of cardiac/fetal alpha-actin in human cardiomyocytes and regenerating skeletal muscle cells

We describe three murine monoclonal antibodies (mAbs) raised against a synthetic decapeptide representing the aminoterminal sequence of the cardiac/ fetal isoform of sarcomeric alpha-actin. When used for immunoblotting or histological immunolocalization, these mAbs distinguish cardiac/fetal alpha-actin from skeletal muscle alpha-actin, and also from all other actin isoforms. We show, by immunofluorescence and immunoperoxidase microscopy of tissue sections, that cardiac/fetal alpha-actin can be localized not only in cardiomyocytes but also in skeletal muscles and their satellite cells during regeneration. These mAbs are potentially valuable in developmental biology, for the characterization of tissue and cultured myogenic cells, in pathology, and for serodiagnosis.

Hybrid proteins between Pseudomonas aeruginosa exotoxin A and poliovirus 2Apro cleave p220 in HeLa cells

Cleavage of p220, a component of the initiation factor eIF-4F, has been correlated with the inhibition of host translation during poliovirus infection. To obtain p220 cleavage in the absence of any other poliovirus gene products, hybrid proteins containing Pseudomonas aeruginosa exotoxin A and poliovirus protease 2Apro have been constructed. The addition of the hybrid molecules to cultured cells did not lead to substantial p220 cleavage. However, the simultaneous presence of the hybrid toxin with replicationally inactive chicken adenovirus particles results in efficient cleavage of p220 in the intact cells. Under these conditions, cellular translation continues unabated for several hours, arguing against a direct requirement for intact p220 in each round of the initiation of translation of cellular mRNAs.

Cloning, expression, and chromosomal localization of the rat mitochondrial capsule selenoprotein gene (MCS): the reading frame does not contain potential UGA selenocysteine codons

The mitochondrial capsule selenoprotein (MCS) is a selenium-containing polypeptide. It is one of three proteins that are important for the maintenance and stabilization of the crescent structure of the sperm mitochondria. In this paper, we report the isolation and characterization of the rat MCS cDNA and gene. The cDNA contains a reading frame for a 145-amino-acid protein and it lacks the UGA codons, which have been found in the reading frame of the mouse MCS cDNA and have been presumed to encode the selenocysteine in the amino terminal of the deduced mouse amino acid sequence. The deduced amino acid sequence of the rat and mouse MCS shows a high level of homology (79%). The rat MCS gene contains two exons; the intron sequence interrupts the 5' untranslated sequence at the same position as in the mouse MCS gene. The transcription start site is located 184 bp upstream of the translation start site. Alignment of the 5'-flanking regions of the mouse and rat genes reveals that the first 400 nucleotides upstream of the transcription start site exhibit an overall sequence similarity of 73%. This conserved region contains no TATA or CAAT box motifs. Northern blot analysis indicates that the MCS mRNA is detectable only in the testis after day 30 of postnatal development. Moreover, in situ hybridization revealed that the rat MCS gene is mainly expressed in round spermatids. From the analysis of mouse-rat cell hybrids that segregate rat chromosomes, the MCS gene was assigned to rat chromosome 2.

Nucleotide substitution type dependence of generation time effect of molecular evolution

Using DNA sequence data of 18 genes from 14 mammals, we analyzed how the average molecular evolution rate per year per site (Vy) depends on the generation time (g). (I) Assuming the relation Vy varies; is directly proportional to g(-alpha), the index of generation time effect, (alpha) was estimated to be about 0.14 for amino acid replacement substitutions (A), and about 0.32 for synonymous substitutions (S). (II) Assuming the relation Vy = V(m)g g-1 + V(e)y, where V(m)g and V(e)y are constant independent of g, the fraction, r(e) = V(e)y/Vy, of the mutation rate independent part (V(e)y) in the total evolution rate (Vy) was estimated under the assumptions of the star phylogeny and the constancy of the mutation rate per generation. r(e) was smallest for mouse with the shortest generation time among our analyzed species, and it was estimated to be about 0.57 for A and 0.31 for S. Both results do not support the view that Vy is equal to the neutral mutation rate per site both for A and for S. They are in line with the thesis that, at least for A and probably even for S, the molecular evolution rate is influenced by some causes other than the mutation rate, such as changing environment.

A human cDNA coding for the Leydig insulin-like peptide (Ley I-L)

cDNA clones for the human Leydig insulin-like peptide (Ley I-L) have been isolated and characterized. The nucleotide sequence of the 743-bp cDNA includes an incomplete 7-bp 5'-noncoding region, an open reading frame of 393 bp, and a 343-bp 3'-noncoding region. By primer extension analysis, the transcription start site was determined as being 14-bp upstream of the translation start site. The underlying gene is expressed in the testis but not in other organs. From the cDNA sequence, it can be deduced that the Ley I-L protein is synthesized as a 131-amino-acid (aa) preproprotein and that it contains a 24-aa signal peptide. Comparison of the pro Ley I-L protein with members of the insulin-like hormone superfamily predicts that the biologically active hormone, after proteolytic processing of the C peptide, consists of a 31-aa long B chain and a 26-aa long A chain, and that it has a molecular weight of 6.25 kDa.

Cloning and expression of a novel human profilin variant, profilin II

We have isolated a 1.7 kbp cDNA encoding a 140 amino acid protein (15.1 kDa, pI 5.91) with a high sequence similarity (62%) to human profilin (profilin I). We have termed this variant profilin II. Northern blot analysis showed that profilin II is highly expressed in brain, skeletal muscle and kidney and less strongly in heart, placenta, lung and liver. In addition, three different transcript lengths were detected. Only one transcript of profilin I was found. The expression level of this was low in brain and skeletal muscle, medium in heart and high in placenta, lung, liver and kidney.

Re-localization of Actsk-1 to mouse chromosome 8, a new region of homology with human chromosome 1

We present here the genetic mapping of the alpha-skeletal actin locus (Actsk-1) on mouse Chromosome (Chr) 8, on the basis of the PCR analysis of a microsatellite in an interspecific backcross. Linkage and genetic distances were established for four loci by analysis of 192 (or 222) meiotic events and indicated the following gene order: (centromere)-Es-1-11.7 cM-Tat-8.3 cM-Actsk-1-0.5 cM-Aprt. Mapping of ACTSK to human Chr 1 and of TAT and APRT to human Chr 16 demonstrates the existence of a new short region of homology between mouse Chr 8 and human Chr 1. Intermingling on this scale between human and mouse chromosomal homologies that occurred during evolution creates disorders in comparative linkage studies.

Alterations of the c-erbB2 gene in human breast cancer

DNA amplification, RNA overexpression and p185 protein expression of the c-erbB2 oncogene were investigated in 109 cases of breast cancer with the aim of evaluating any correlation between the different methods. A correlation between Southern blotting and immunohistochemical analysis of paraffin-embedded material was found. Thus, amplification of the c-erbB2 oncogene leads to overexpression of the p185 protein. By contrast, no statistical correlation could be shown between RNA overexpression, measured by Northern blotting, and immunohistochemical p185 membrane stainings. It is of special interest that most of the cases that are positive for Northern blotting and negative for immunochemistry are negative for Southern blotting as well. Contradictory findings between RNA overexpression and lack of immunohistochemical staining of p185 give rise to the assumption that a defective protein is encoded, which cannot be incorporated into the substructures of the tumour cell membrane. When screening for point mutations in the transmembrane domain of the c-erbB2 oncogene, no point mutation could be detected, either by using the endonuclease FokI, which cuts at position 2012 (the point mutation in the neu gene of the rat), or by direct sequencing.

Biosynthesis of hepatic corticosteroid-binding globulin: ontogeny and effect of thyroid hormone

The present study reports on the ontogeny and the effect of thyroid hormones on liver corticosteroid-binding globulin (CBG) biosynthesis, in relation to plasma CBG binding capacity in the rat. We show that mRNACBG contents were high in liver of 18-day-old fetuses and decreased with age to reach almost undetectable levels by postnatal day 1. Interestingly, at the latter time point plasma CBG concentration remained elevated and disappeared thereafter from the circulation with a half-life of about 3 days. The messenger was localized in parenchymatous cells and not in hematopoietic ones, although the latter constitute the major cell population in fetal liver. It is not until after 10 days of age that mRNACBG and plasma CBG levels increased in concert, with a sex-difference being noticed by postnatal day 30. Treatment of rats with 3,3',5-triiodo-L-thyronine (T3), but not reverse T3 (rT3) (the predominant form present in fetal serum), enhanced CBG biosynthesis. These findings show that liver mRNACBG contents undergo dramatic changes during ontogeny and suggest the existence of a differential regulation of the messenger in fetal and neonatal rats.

An STS in the human skeletal alpha-actin gene

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Structure, chromosome location, and expression of the human smooth muscle (enteric type) gamma-actin gene: evolution of six human actin genes

Recombinant phages that carry the human smooth muscle (enteric type) gamma-actin gene were isolated from human genomic DNA libraries. The amino acid sequence deduced from the nucleotide sequence matches those of cDNAs but differs from the protein sequence previously reported at one amino acid position, codon 359. The gene containing one 5' untranslated exon and eight coding exons extends for 27 kb on human chromosome 2. The intron between codons 84 and 85 (site 3) is unique to the two smooth muscle actin genes. In the 5' flanking region, there are several CArG boxes and E boxes, which are regulatory elements in some muscle-specific genes. Hybridization with the 3' untranslated region, which is specific for the human smooth muscle gamma-actin gene, suggests the single gene in the human genome and specific expressions in enteric and aortic tissues. From characterized molecular structures of the six human actin isoform genes, we propose a hypothesis of evolutionary pathway of the actin gene family. A presumed ancestral actin gene had introns at least sites 1, 2, and 4 through 8. Cytoplasmic actin genes may have directly evolved from it through loss of introns at sites 5 and 6. However, through duplication of the ancestral actin gene with substitutions of many amino acids, a prototype of muscle actin genes had been created. Subsequently, striated muscle actin and smooth muscle actin genes may have evolved from this prototype by loss of an intron at site 4 and acquisition of a new intron at site 3, respectively.

Distribution and activity of alternatively spliced Alzheimer amyloid peptide precursor and scrapie PrP mRNAs on rat brain polysomes

Mammalian brains contain low levels of the Alzheimer amyloid precursor variants (AAPPs) and the normal form of the scrapie agent protease-resistant protein (PrPc); however, their mRNAs are readily detectable. To understand these discrepancies we have investigated some aspects of the translational regulation of these mRNAs. An accurate blot-hybridization procedure was developed to measure absolute amounts of mRNA. Rat brain contains the following mRNA levels (ng/g tissue) AAPP(695), 170; AAPP(751/770), 63; PrPc, 144; actin, 615; glyceraldehyde-3-phosphate dehydrogenase (G3PDH), 359; ferritin, 148. The method was also used to determine the distribution of mRNAs between translationally active polysomes and translationally inactive ribonucleoprotein protein particles (mRNPs). More than 90% of G3PDH and actin mRNAs were associated with polysomal RNA; whereas, ferritin light chain mRNA was predominantly (90%) in mRNP RNA. The degree of cross-contamination of mRNPs with polysomes was less than 10%. Probes specific for the scrapie PrP protein and the AAPP(695) splice junction revealed that 70% of these mRNAs were associated with polysomes. One-half of AAPP(751/770) mRNAs (which comprise 20-30% of all AAPP mRNA in brain) were found in polysomes. We conclude therefore that both scrapie and AAPP mRNAs are subject to translational regulation in rat brain. Evidence from in vitro translational experiments confirm the message distribution determined by blot hybridization and corroborate the hypothesis that AAPP is subject to partial post-transcriptional regulation. Nevertheless, the low tissue levels of AAPP and PrPc must result primarily from their relatively rapid turnover.

Structure, chromosome location, and expression of the human smooth muscle (enteric type) gamma-actin gene: evolution of six human actin genes

Recombinant phages that carry the human smooth muscle (enteric type) gamma-actin gene were isolated from human genomic DNA libraries. The amino acid sequence deduced from the nucleotide sequence matches those of cDNAs but differs from the protein sequence previously reported at one amino acid position, codon 359. The gene containing one 5' untranslated exon and eight coding exons extends for 27 kb on human chromosome 2. The intron between codons 84 and 85 (site 3) is unique to the two smooth muscle actin genes. In the 5' flanking region, there are several CArG boxes and E boxes, which are regulatory elements in some muscle-specific genes. Hybridization with the 3' untranslated region, which is specific for the human smooth muscle gamma-actin gene, suggests the single gene in the human genome and specific expressions in enteric and aortic tissues. From characterized molecular structures of the six human actin isoform genes, we propose a hypothesis of evolutionary pathway of the actin gene family. A presumed ancestral actin gene had introns at least sites 1, 2, and 4 through 8. Cytoplasmic actin genes may have directly evolved from it through loss of introns at sites 5 and 6. However, through duplication of the ancestral actin gene with substitutions of many amino acids, a prototype of muscle actin genes had been created. Subsequently, striated muscle actin and smooth muscle actin genes may have evolved from this prototype by loss of an intron at site 4 and acquisition of a new intron at site 3, respectively.

Post-translational processing of the amino terminus affects actin function

We have studied the importance of N-terminal processing for normal actin function using the Drosophila Act88F actin gene transcribed and translated in vitro. Despite having different charges as determined by two-dimensional (2D) gel electrophoresis, Act88F expressed in vivo and in vitro in rabbit reticulocyte lysate bind to DNase I with equal affinity and are able to copolymerise with bulk rabbit actin equally well. Using peptide mapping and thin-layer electrophoresis we have shown that bestatin [( 3-amino-2-hydroxy-4-phenyl-butanoyl]-L-leucine), an inhibitor of aminopeptidases, can inhibit actin N-terminal processing in rabbit reticulocyte lysate. Although processed and unprocessed actins translated in vitro are able to bind to DNase I equally well, unprocessed actins are less able to copolymerise with bulk actins. This effect is more pronounced when bulk rabbit actin is used but is still seen with bulk Lethocerus actin. Also, the unprocessed actins reduce the polymerisation of the processed actin translated in vitro with the bulk rabbit actin. This suggests that individual actins do interact, even in non-polymerising conditions. The reduced ability of unprocessed actin to polymerise shows that correct post-translational modification of the N terminus is required for normal actin function.

Scrambled exons

Using a sensitive assay for RNA expression, we identified several abnormally spliced transcripts in which exons from a candidate tumor suppressor gene (DCC) were scrambled during the splicing process in vivo. Cloning and sequencing of PCR-amplified segments of the abnormally spliced transcripts showed that exons were joined accurately at consensus splice sites, but in an order different from that present in the primary transcript. Four scrambled transcripts were identified, each involving a different pair of exons. The scrambled transcripts were found at relatively low levels in a variety of normal and neoplastic cells of rodent and human origin, primarily in the nonpolyadenylated component of cytoplasmic RNA. These results demonstrate that the splicing process does not always pair sequential exons in the order predicted from their positions in genomic DNA, thus creating a novel type of RNA product.

Characterization of a cDNA coding for rat glutamic acid decarboxylase

cDNA clones have been isolated for rat glutamic acid decarboxylase (glutamate decarboxylase; EC 4.1.1.15) (GAD) and 3216 bp of the sequence have been determined. This sequence extends the previously reported feline GAD cDNA sequence both in the 5' (67 bp) and 3' (887 bp) directions and contains the polyadenylation signal and tail. The cDNA codes for a 67 kDa mol. wt. protein beginning from the putative initiator methionine found in the feline sequence. Extensive homology to feline GAD was identified at the amino acid level (97% identity) within the coding region. This interspecies homology is high compared to other neurotransmitter synthesizing enzymes and suggests selective pressure to maintain the primary sequence throughout the full length of the protein. Homology is found 5' to the putative initiator methionine. Extensive stretches of homology are also found in the 3' non-coding region. These conserved non-coding regions may play a role in GAD mRNA regulation. The rat cDNA sequence will facilitate investigations into the structure and regulation of the GAD gene.

Genes of Acanthamoeba: DNA, RNA and protein sequences (a review)

This review summarizes knowledge about the structure of nuclear genes and mitochondrial DNA in Acanthamoeba. The information about nuclear genes is derived from studies of DNA, RNA and protein sequences. The genes considered are those for 5S, 5.8S and 18S rRNA, actin I, profilins Ia/b and II, myosins IB, IC and II, and calmodulin. All of the sequences show strong similarities to comparable sequences from other organisms. Introns have been found in the actin and myosin genes. The location of the actin intron is unique, but many of the myosin introns occur at the same sites as introns in myosins of other organisms. Sequence comparisons, especially of 5S and 5.8S rRNA and actin, support previous evidence, based primarily on 18S rRNA, that Acanthamoeba genes are at least as closely related to those of higher plants and animals as they are to various other protistan genera. The functional organization of the promoter region for the nuclear rDNA transcription unit has been studied extensively, but there is a need for information about the functional organization of regulatory sequences for other genes. Restriction fragment length profile (RFLP) studies of mitochondrial DNA reveal relatively high levels of overall sequence diversity, but information on the structure and function of individual genes is needed. The RFLP appear to have potential as tools for taxonomic studies of this genus.

A bovine homolog to the human myogenic determination factor myf-5: sequence conservation and 3' processing of transcripts

A bovine cDNA library from fetal skeletal muscle myoblasts. was screened with a 274 bp probe to a conserved region of the mouse MyoD1 cDNA. One positive recombinant, designated bmyf, was found to contain a 1931 bp insert with an open reading frame encoding a predicted protein highly related to the human myogenic factor myf-5 Human and bovine factors are 96% homologous in their predicted amino acid sequences. At the nucleotide level, bmyf and myf-5 are 92% identical in the coding region and 74 and 80% homologous in their 5'- and 3'-untranslated regions, respectively. The bmyf cDNA, nevertheless, extends 475 nucleotides beyond a polyadenylation signal common to both cDNAs. Bmyf transcripts are expressed exclusively in skeletal muscle where three transcripts of 1.5, 2 and 3 kb were detected. While the 1.5 kb transcript lacks sequences 3' to the polyadenylation signal at nt 1415 in the bmyf cDNA, both the 2 and 3 kb RNAs contain these sequences suggesting that bmyf transcripts are alternatively polyadenylated. Bmyf cDNA can activate the expression of the myogenic program in C3H10T1/2 fibroblasts as assayed by stable and transient transfection experiments.

Cloning and expression of cDNA and genomic clones encoding three delayed rectifier potassium channels in rat brain

Rat brain cDNA and genomic clones encoding three K+ channels, Kv1, Kv2, and Kv3, have been isolated by screening with Shaker probes and encode proteins of 602, 530, and 525 amino acids. Each of the deduced protein sequences contains six hydrophobic domains (including an S4-type region characteristic of many voltage-gated channels) and are 68%-72% identical to each other overall. Transcripts of approximately 3.5, approximately 6.5, and approximately 9.5 kb encode Kv1, Kv2, and Kv3, respectively. The Kv2 mRNA is expressed only in brain, whereas the Kv1 and Kv3 transcripts are found in several other tissues as well. There is a marked increase in the amount of Kv1 mRNA in cardiac tissue during development and a similar, but less pronounced, increase of both this mRNA and the Kv2 transcript in brain. RNAs synthesized in vitro from the three clones induce voltage- and time-dependent, delayed rectifier-like K+ currents when injected into Xenopus oocytes, demonstrating that they encode functional K+ channels.

Structure of 3'-downstream segment of the human smooth muscle (aortic-type) alpha-actin-encoding gene and isolation of the specific DNA probe

We isolated the 3'-downstream part of the human aortic smooth muscle alpha-actin (SM alpha A)-encoding gene and determined the nucleotide sequence, including the ninth (last) exon and 3'-untranslated (UT) region. From the comparison of the human 3'-UT region with rat and chicken 3'-UT regions, its homology is lower than those in 3'-UT regions of other actin isoforms such as cardiac alpha-actin and cytoskeletal beta-actin. Therefore, by using the 3'-UT region of the human SM alpha A gene as an actin isoform-specific probe, this gene was detected as a single copy only in the human genome, which expressed the 1.7-kb RNA transcript in an aortic tissue-specific manner.

Brain capillary 46,000 dalton protein is cytoplasmic actin and is localized to endothelial plasma membrane

The most abundant protein of the brain capillary, which makes up the blood-brain barrier (BBB) in vivo, is a protein that migrates at a molecular weight of approximately 46 kDa on sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The bovine brain capillary 46 kDa protein was purified by SDS-PAGE and Sephadex G-25 gel filtration. The purified protein migrated as a single band of molecular weight of approximately 42,000 Da on subsequent SDS-PAGE followed by silver staining. The protein was digested by trypsin and tryptic peptides were analyzed by reverse phase high-performance liquid chromatography (HPLC). Two of these peptides, 11 and 18 amino acids in length, were sequenced and found to be identical to amino acid sequences corresponding to portions of cytoplasmic actin. The SDS-PAGE gel-purified 46 kDa protein was also subjected to limited proteolysis using S. aureus V8 protease, and this resulted in the formation of a prominent 31 kDa doublet as well as smaller proteolytic fragments, and these fragments were of identical molecular weight to those generated from limited proteolysis of bovine actin. Electron microscopic immunoperoxidase studies with primary cultures of bovine brain capillary endothelium showed that immunoreactive actin is intimately associated with the plasma membranes. In conclusion, the brain capillary 46 kDa protein is cytoplasmic actin and is localized to the endothelial plasma membrane. Modulations of brain capillary endothelial actin may play a role in the regulation of BBB permeability.

Identification and developmental expression of a smooth-muscle gamma-actin in postmeiotic male germ cells of mice

Mouse testis contains two size classes of actin mRNAs of 2.1 and 1.5 kilobases (kb). The 2.1-kb actin mRNA codes for cytoplasmic beta- and gamma-actin and is found throughout spermatogenesis, while the 1.5-kb actin mRNA is first detected in postmeiotic cells. Here we identify the testicular postmeiotic actin encoded by the 1.5-kb mRNA as a smooth-muscle gamma-actin (SMGA) and present its cDNA sequence. The amino acid sequence deduced from the postmeiotic actin cDNA sequence was nearly identical to that of a chicken gizzard SMGA, with one amino acid replacement at amino acid 359, where glutamine was substituted for proline. The nucleotide sequence of the untranslated region of the SMGA differed substantially from those of other isotypes of mammalian actins. By using the 3' untranslated region of the testicular SMGA, a highly specific probe was obtained. The 1.5-kb mRNA was detected in RNA from mouse aorta, small intestine, and uterus, but not in RNA isolated from mouse brain, heart, and spleen. Testicular SMGA mRNA was first detected and increased substantially in amount during spermiogenesis in the germ cells, in contrast to the decrease of the cytoplasmic beta- and gamma-actin mRNAs towards the end of spermatogenesis. Testicular SMGA mRNA was present in the polysome fractions, indicating that it was translated. These studies demonstrate the existence of an SMGA in male haploid germ cells. The implications of the existence of an SMGA in male germ cells are discussed.

Molecular cloning of preproacrosin and analysis of its expression pattern in spermatogenesis

Complementary DNA clones for the boar preproacrosin have been isolated from a randomly primed testis cDNA library in lambda gt10 and from an oligo(dT)-primed testis cDNA in lambda gt11. The nucleotide sequence of the 1418-bp cDNA insert includes a 46-bp 5'-untranslated region, an open reading frame of 1248 bp corresponding to 416 amino acids (45.59 kDa) and a 121-bp 3'-untranslated region. The deduced amino acid sequence includes the active-site residues histidine, asparagine and serine of the catalytic triad of the serine proteinase super-family and is colinear with that determined by amino acid sequencing of the boar acrosin light chain and of a small region of the NH2-terminal sequence of the heavy chain. The preproacrosin cDNA contains at the 3' end a 381-bp sequence which codes for an amino acid sequence not yet found in any other serine proteinase. This amino acid sequence is rich in proline (42 out of 127 amino acids) and is suggested to be involved in the recognition and binding of the spermatozoa to the zona pellucida of the ovum. The mRNA for preproacrosin is synthesized as an approximately 1.6-kb-long molecule only in the postmeiotic stages of boar and bull spermatogenesis.

Cloning and characterization of a cDNA for the B beta chain of rat fibrinogen: evolutionary conservation of translated and 3'-untranslated sequences

A cDNA clone for the B beta chain of rat fibrinogen has been isolated and characterized. The cDNA insert is 1023 bp in length and corresponds to the 3' half of the B beta chain mRNA. The cDNA represents 890 bp of the coding sequence for the C-terminal half of the B beta chain and 133 bp of the 3'-untranslated region. The coding sequence for this region of the rat cDNA shares a high degree of identity with the corresponding regions of the human and bovine B beta-chain cDNAs and a moderate degree of identity with the corresponding region of the lamprey B beta-chain cDNA. A comparison of the amino acid sequences deduced from these cDNAs reveals three regions which share extensive identity among all four sequences. Two additional regions are identified which share extensive identity among the three mammalian sequences and significant identity with the lamprey sequence. These regions appear to represent distinct functional domains. Possible functions for these domains are briefly discussed. A high degree of identity also exists between the 3'-untranslated regions of the three mammalian cDNAs, suggesting that this region of the mRNA, although noncoding, is functionally important.

Identification and developmental expression of a smooth-muscle gamma-actin in postmeiotic male germ cells of mice

Mouse testis contains two size classes of actin mRNAs of 2.1 and 1.5 kilobases (kb). The 2.1-kb actin mRNA codes for cytoplasmic beta- and gamma-actin and is found throughout spermatogenesis, while the 1.5-kb actin mRNA is first detected in postmeiotic cells. Here we identify the testicular postmeiotic actin encoded by the 1.5-kb mRNA as a smooth-muscle gamma-actin (SMGA) and present its cDNA sequence. The amino acid sequence deduced from the postmeiotic actin cDNA sequence was nearly identical to that of a chicken gizzard SMGA, with one amino acid replacement at amino acid 359, where glutamine was substituted for proline. The nucleotide sequence of the untranslated region of the SMGA differed substantially from those of other isotypes of mammalian actins. By using the 3' untranslated region of the testicular SMGA, a highly specific probe was obtained. The 1.5-kb mRNA was detected in RNA from mouse aorta, small intestine, and uterus, but not in RNA isolated from mouse brain, heart, and spleen. Testicular SMGA mRNA was first detected and increased substantially in amount during spermiogenesis in the germ cells, in contrast to the decrease of the cytoplasmic beta- and gamma-actin mRNAs towards the end of spermatogenesis. Testicular SMGA mRNA was present in the polysome fractions, indicating that it was translated. These studies demonstrate the existence of an SMGA in male haploid germ cells. The implications of the existence of an SMGA in male germ cells are discussed.

Heterogeneity in the molecular defect leading to the leukocyte adhesion deficiency

Leukocyte adhesion deficiency (LAD) is a recessive autosomal disease characterized by life-threatening recurrent bacterial infections, by defective functions of leukocytes and by deficient membrane expression of leukocyte adhesion glycoproteins. These proteins, LFA-1, Mac-1 and p150,95, are alpha 1/beta 1 heterodimers composed of different alpha chains and of a common beta chain. Patients with the severe phenotype of the disease completely lack the three glycoproteins on cell surface. Previous studies showed a conserved synthesis of the LFA-1 alpha chain precursor in cytosol of patients' cells and an inconstant presence of the beta chain precursor. When present, precursors are in free form and not associated to alpha/beta complexes in the cells of patients with the severe phenotype. The availability of the beta chain cDNA probe allowed us to examine the beta chain gene expression in the lymphoblastoid cell lines of 4 patients. On the basis of the results obtained both at protein and RNA levels we can distinguish 3 types of mutations characterized by (a) barely detectable beta subunit messenger RNA and undetectable beta precursor, (b) decreased level of beta subunit mRNA and undetectable beta precursor and (c) normal beta subunit mRNA level and detectable beta precursor of normal size.

A third striated muscle actin gene is expressed during early development in the amphibian Xenopus laevis

During early embryonic development in the frog Xenopus laevis, several muscle-specific actin genes encoding distinct actin protein isoforms are activated in cells of the embryonic muscle. In addition to the cardiac (or alpha 1) and skeletal (or alpha 2) actin genes, a third muscle-specific actin gene is expressed in the same embryonic tissue. We have determined the complete nucleotide sequence of this third gene and examined its expression in embryonic and adult tissues. During embryogenesis, this femoral (alpha 3) actin gene is activated several hours later than its cardiac and skeletal counterparts and its transcripts are first detected after neurulation. The gene encodes a skeletal-type actin protein and is expressed exclusively in skeletal muscle in the adult frog. Two copies of this gene have been isolated from the tetraploid species Xenopus laevis, differing by only a few nucleotides in their protein-coding sequence. The related, diploid species, Xenopus tropicalis, possesses a single copy of the alpha 3 gene and its transcript is similarly conserved in nucleotide sequence. However, the X. tropicalis gene is expressed exclusively in embryonic stages of development. Comparison of the X. laevis and X. tropicalis alpha 3 gene promoters reveals extensive sequence homology, including several copies of a repeated motif that is common to other vertebrate striated-muscle actin gene promoters.

Multiple 5'-flanking regions of the human alpha-skeletal actin gene synergistically modulate muscle-specific expression

Transfection into myogenic and nonmyogenic cell lines was used to investigate the transcriptional regulation of the human alpha-skeletal actin gene. We demonstrated that 1,300 base pairs of the 5'-flanking region directed high-level transient expression of the bacterial chloramphenicol acetyltransferase gene in differentiated mouse C2C12 and rat L8 myotubes but not in mouse nonmuscle L.TK- and HuT-12 cells. Unidirectional 5' deletion analysis and heterologous promoter stimulation experiments demonstrated that at least three transcription-regulating subdomains lie in this 1,300-base-pair region. A proximal cis-acting transcriptional element located between positions -153 and -87 relative to the start of transcription at +1 was both sufficient and necessary for muscle-specific expression and developmental regulation during myogenesis in the two myogenic cell systems. The region 3' of position -87 interacted with factors present in both myogenic and fibroblastic cells and appeared to define, or to be a major component of, the basal promoter. In C2C12 myotubes, but not in L8 myotubes, a distal sequence domain between positions -1300 and -626 and the proximal sequence domain between positions -153 and -87 each induced transcription about 10-fold and synergistically increased CAT expression 100-fold over levels achieved by the sequences 3' of position -87. Furthermore, these cis-acting elements independently and synergistically modulated an enhancerless, heterologous simian virus 40 promoter in a tissue-specific manner. DNA fragments which included the proximal domain displayed classical enhancerlike properties. The central region between positions -626 and -153, although required in neither cell line, had a positive, two- to threefold, additive role in augmenting expression in L8 cells but not in C2C12 cells. This suggests that certain elements between positions -1300 and -153 appear to be differentially utilized for maximal expression in different myogenic cells and that the particular combination of domains used is dependent on the availability, in kind or amount, of trans-acting, transcription-modulating factors present in each cell type. Thus, multiple myogenic factors that vary qualitatively and quantitatively may be responsible for the different and complex modulatory programs of actin gene expression observed during in vivo muscle differentiation.

Cytoskeletal actin gene families of Xenopus borealis and Xenopus laevis

We have sequenced the coding and leader regions, as well as part of the 3' untranslated region, of a Xenopus borealis type 1 cytoskeletal actin gene [defined according to the arrangement of acidic residues at the N-terminus; Vandekerckhove et al. (1981) J Mol Biol 152:413-426]. The encoded amino acid sequence is the same as the avian and mammalian beta (type 1) cytoskeletal actins, except for an isoleucine at position 10 (as found in the mammalian gamma cytoskeletal actins), and an extra amino acid, alanine, after the N-terminal methionine. Five introns were found, in the same positions as those of the rat and chicken beta-actin genes. The 5' and 3' untranslated regions resemble those of the human gamma (type 8) cytoskeletal actin gene more closely than the mammalian beta genes. Primer extension showed that this type 1 gene is transcribed in ovary and tadpole. Sequencing of primer extension products demonstrated two additional mRNA species in X. borealis, encoding type 7 and 8 isoforms. This contrasts with the closely related species Xenopus laevis, where type 4, 5, and 8 isoforms have been found. The type 7 isoform has not previously been found in any other species. The mRNAs of the X. borealis type 1 and 8 and X. laevis type 5 and 8 isoforms contain highly homologous leaders. The X. borealis type 7 mRNA has no leader homology with the other mRNA species and, unlike them, has no extra N-terminal alanine codon. The evolutionary implications of these data are discussed.

Multiple 5'-flanking regions of the human alpha-skeletal actin gene synergistically modulate muscle-specific expression

Transfection into myogenic and nonmyogenic cell lines was used to investigate the transcriptional regulation of the human alpha-skeletal actin gene. We demonstrated that 1,300 base pairs of the 5'-flanking region directed high-level transient expression of the bacterial chloramphenicol acetyltransferase gene in differentiated mouse C2C12 and rat L8 myotubes but not in mouse nonmuscle L.TK- and HuT-12 cells. Unidirectional 5' deletion analysis and heterologous promoter stimulation experiments demonstrated that at least three transcription-regulating subdomains lie in this 1,300-base-pair region. A proximal cis-acting transcriptional element located between positions -153 and -87 relative to the start of transcription at +1 was both sufficient and necessary for muscle-specific expression and developmental regulation during myogenesis in the two myogenic cell systems. The region 3' of position -87 interacted with factors present in both myogenic and fibroblastic cells and appeared to define, or to be a major component of, the basal promoter. In C2C12 myotubes, but not in L8 myotubes, a distal sequence domain between positions -1300 and -626 and the proximal sequence domain between positions -153 and -87 each induced transcription about 10-fold and synergistically increased CAT expression 100-fold over levels achieved by the sequences 3' of position -87. Furthermore, these cis-acting elements independently and synergistically modulated an enhancerless, heterologous simian virus 40 promoter in a tissue-specific manner. DNA fragments which included the proximal domain displayed classical enhancerlike properties. The central region between positions -626 and -153, although required in neither cell line, had a positive, two- to threefold, additive role in augmenting expression in L8 cells but not in C2C12 cells. This suggests that certain elements between positions -1300 and -153 appear to be differentially utilized for maximal expression in different myogenic cells and that the particular combination of domains used is dependent on the availability, in kind or amount, of trans-acting, transcription-modulating factors present in each cell type. Thus, multiple myogenic factors that vary qualitatively and quantitatively may be responsible for the different and complex modulatory programs of actin gene expression observed during in vivo muscle differentiation.

Entamoeba histolytica: cloning and characterization of actin cDNA

In order to study gene expression in the human parasite Entamoeba histolytica, a cDNA library of E. histolytica strain 200:NIH was constructed using the phage vector lambda gt10. Three cDNA clones (A, B and C) were selected for further analysis. Each of the three clones hybridized to a distinct mRNA. Two of these mRNAs were translated in vitro after hybrid selection, and yielded distinct translation products. One of these mRNAs, selected by hybridization to clone A, encodes the most abundantly expressed protein in E. histolytica. DNA sequence analysis of this cDNA clone identified the DNA as that encoding actin. The deduced amino acid sequence of E. histolytica actin resembles both cytoplasmic and muscle actins and has an unusual N-terminal glycine residue. We have shown that a family of actin genes is present in E. histolytica. Six different E. histolytica actin clones were obtained from a lambda gt10 genomic library using subcloned cDNA probes. Southern analysis of three different E. histolytica strains (200:NIH, Rhaman, and HM-1:IMSS) revealed at least four different actin genes. Strain HM-1:IMSS, however, differs by the presence of an additional actin gene.

Genomic and cDNA actin sequences from a virulent strain of Entamoeba histolytica

Invasiveness of Entamoeba histolytica strains that cause acute amoebiasis is characterized by aggressive behavior associated with cell motility and actin function. Analysis of actin genes from E. histolytica was initiated by devising methods for the isolation of biologically active nucleic acids, which allowed the preparation of cDNA and genomic DNA libraries. E. histolytica actin-encoding cDNAs and genomic clones have been isolated from libraries prepared from the virulent HM1:IMSS strain using a heterologous actin probe. Nucleotide sequence analysis of three independent cDNA clones and one genomic clone reveals a highly unusual codon bias and the absence of intervening sequences in E. histolytica actin. The coding sequence of the genomic clone is identical to that of two of the three cDNA clones. These represent at least two distinct mRNAs differing only by five silent changes in the protein coding sequence. Multiple genomic copies of the actin gene can be detected by Southern hybridization. E. histolytica actin exhibits a higher degree of homology to cytoplasmic than to muscle actin. Although the protein has been shown not to bind DNase I, the inferred amino acid sequence indicates conservation of all residues implied to participate in this binding.

The complete sequence of the mouse skeletal alpha-actin gene reveals several conserved and inverted repeat sequences outside of the protein-coding region

The complete nucleotide sequence of a genomic clone encoding the mouse skeletal alpha-actin gene has been determined. This single-copy gene codes for a protein identical in primary sequence to the rabbit skeletal alpha-actin. It has a large intron in the 5'-untranslated region 12 nucleotides upstream from the initiator ATG and five small introns in the coding region at codons specifying amino acids 41/42, 150, 204, 267, and 327/328. These intron positions are identical to those for the corresponding genes of chickens and rats. Similar to other skeletal alpha-actin genes, the nucleotide sequence codes for two amino acids, Met-Cys, preceding the known N-terminal Asp of the mature protein. Comparison of the nucleotide sequences of rat, mouse, chicken, and human skeletal muscle alpha-actin genes reveals conserved sequences (some not previously noted) outside of the protein-coding region. Furthermore, several inverted repeat sequences, partially within these conserved regions, have been identified. These sequences are not present in the vertebrate cytoskeletal beta-actin genes. The strong conservation of the inverted repeat sequences suggests that they may have a role in the tissue-specific expression of skeletal alpha-actin genes.