Isolation, sequence and molecular karyotype analysis of the actin gene of Cryptosporidium parvum.

Actin is an ubiquitous and highly conserved microfilament protein which is hypothesized to play a mechanical, force-generating role in the unusual gliding motility of sporozoan zoites and in their active penetration of host cells. We have identified and isolated an actin gene from a Cryptosporidium parvum genomic DNA library using a chicken beta-actin cDNA as an hybridization probe. The nucleotide sequences of two overlapping recombinant clones were identical and the amino acid sequence deduced from the single open reading frame was 85 % identical to the P. falciparum actin I and human gamma-actin proteins. The predicted 42 106-Da Cryptosporidium actin contains 376 amino acids and is encoded by a single-copy gene which contains no introns. The nucleic acid coding sequence is 72% biased to the use of A or T in the third position of codons. Chromosome-sized DNA released from intact C. parvum oocysts was resolved by OFAGE into 5 discrete ethidium bromide-staining DNAs ranging in size from 900 to 1400 kb; the cloned C. parvum actin gene hybridized to a single chromosomal DNA of approximately 1200 kb.     

Identification and localization of two genes on the chicken Z chromosome: implication of evolutionary conservation of the Z chromosome among avian species

A cDNA clone containing an insert of about 3.4 kb, pCIREBP, was isolated from the chicken liver cDNA library and identified as a clone for the chicken homologue of iron-responsive element-binding protein (IREBP). The deduced amino acid sequence showed 88% identity with that of the mouse IREBP and 17 out of the 20 active site residues of the pig heart mitochondrial aconitase were conserved. Another cDNA clone, pZOV3, containing an insert of about 4.5 kb was isolated from the chicken ovary cDNA library. This cDNA contained an open reading frame for 327 amino acid residues, whose sequence had partial similarity to two immunoglobulin superfamily proteins; mouse GP-70 and chicken HT7. Fluorescencein situ hybridization using corresponding genomic clones revealed that both genes are localized on the Z chromosome; the ZOV3 gene at the middle of the short arm and the IREBP gene at the boundary of heterochromatin on the long arm. Southern blot hybridization to male and female genomic DNA preparations from six species representing five avian genera suggested that these two genes are Z-linked in all the species tested.     

Molecular clones of alpha-tubulin genes of Plasmodium yoelii reveal an unusual feature of the carboxy terminus

By using a Trypanosoma brucei alpha-tubulin cDNA probe under reduced stringency hybridization conditions, we have isolated two genomic clones that constitute portions of alpha-tubulin genes of the rodent malarial parasite Plasmodium yoelii. P. yoelii has two alpha-tubulin genes, the 3' portions of which were present in the two clones, Py alpha T1 and Py alpha T2, containing 1.3 kb and 6.6 kb EcoRI fragments respectively. The 1358 bp Py alpha T1 clone was completely sequenced and found to contain 591 nucleotides of uninterrupted coding sequence with a strong bias for AT-rich codons, starting with codon 254 of a consensus alpha-tubulin sequence. Numerous attempts to clone 5' portions of these genes were unsuccessful. A single mRNA of 2.3 kb was recognized by both the clones in the erythrocytic stages of P. yoelii. A probe constituting the untranslated sequences of Py alpha T1 also recognized this RNA but failed to hybridize with Py alpha T2 sequences, indicating that the gene represented by the Py alpha T1 clone was expressed during the erythrocytic stages. The deduced amino acid sequence of the Py alpha T1 gene terminates in Tyr-Glu instead of Glu-Tyr observed in alpha-tubulins of almost all other organisms. The difference observed may have implications for alpha-tubulin metabolism in malarial parasites.     

Molecular cloning and characterization of actin genes from Echinococcus granulosus

An Echinococcus granulosus genomic library has been screened with a mouse β-actin cDNA probe. Two clones carrying DNA fragments of about 15 kb, possibly derived from the same genome region, have been isolated. This 15-kb genomic region includes 2 actin-related sequences (EgactI and EgactII) separated by about 4 kb. The nucleotide sequences of both genes were determined. The EgactI sequence presents no introns, but an intron of 591 bp was observed in the EgactII sequence. The genes potentially encode 375 and 376 amino-acid-long actins, respectively, with a homology of 85.3%. The deduced amino acid sequences from both genes were compared to the actin sequences from other organisms, showing similarities ranging from 63.5% to 90.6%. The nucleotide sequence of a partial actin cDNA clone has been determined. The deduced amino acids sequence showed a homology of 90.3% and 88.0% in relation to the EgactI and EgactII sequences respectively, suggesting the existence of at least one more actin gene in E. granulosus. This hypothesis is reinforced by the number of bands detected in the Southern blot analysis. Experiments based on the amplification of DNA segments using 3′-specific actin primers indicate that the EgactI gene is transcribed in protoscoleces.     

Structure and organization of the histidine-rich protein gene of Plasmodium lophurae

Recombinant cDNA clones representing the carboxy-terminal portion of the histidine-rich protein of Plasmodium lophurae and the 3' untranslated region of the mRNA have been sequenced. Histidine accounts for 78% of the predicted amino acid sequence. The DNA and protein sequences in this region differ significantly from published sequences deduced from cloned genomic DNA of P. lophurae. Sequence data from two independent cDNA clones, comparison of restriction endonuclease sites present in genomic DNA, genomic and cDNA clones, gene titrations, S1 nuclease digestion of cDNA-mRNA hybrids and comparison of predicted and published data for the amino acid composition of the histidine-rich protein all suggest that P. lophurae contains one histidine-rich protein gene and that the sequence of the 3' coding region of this gene has been correctly deduced from the cDNA clones.     

The tubulin genes of the human malaria parasite Plasmodium falciparum, their chromosomal location and sequence analysis of the alpha-tubulin II gene

We report the isolation and sequencing of genomic clones encompassing the entire alpha-tubulin II gene from the human malaria parasite Plasmodium falciparum. This gene is closely related to, but significant different from the alpha-tubulin I gene that we have described previously. These two genes represent the entire complement of alpha-tubulin sequences in this organism and are expressed in a stage-specific manner. The alpha-II gene is present as a single copy and encodes a tubulin molecule with a predicted length of 450 amino acid residues (49.7 kDa). Like the alpha-I gene, it contains two introns, which are in identical positions to those of alpha-I, but are about one-third smaller. The deduced alpha-II protein is very similar to alpha-tubulin I (94.2% amino acid identity), except for notable differences across residues 40-45. In addition, unlike the great majority of alpha-tubulin genes (including alpha-I), alpha-II does not encode a terminal tyrosine residue. Using pulsed field gel electrophoresis we demonstrate that the two alpha-tubulin genes, together with the single beta-tubulin gene, are unlinked, all residing on different chromosomes. We assign alpha-I to chromosome 9, alpha-II to chromosome 4 and beta-tubulin to chromosome 10.     

Histidine-rich protein genes and their transcripts in Plasmodium falciparum and P. lophurae

The presence of histidine-rich protein (HRP) related genes and gene products in Plasmodium falciparum was demonstrated using a synthetic pentahistidine-encoding oligonucleotide and a cloned HRP cDNA probe prepared from the avian parasite P. lophurae. In Northern blotting experiments, two knobby clones of P. falciparum were found to contain a 3500 nucleotide RNA species that hybridized with the oligonucleotide and HRP cDNA probes. As this component had the expected size for an mRNA encoding an 80-90 kDa protein and was absent from two knobless clones of P. falciparum, we concluded that it represented a 'knob protein' mRNA. Using the restriction enzyme EcoRI, three identical cross-hydribizing HRP gene fragments were found in the DNA of both knobby and knobless clones of P. falciparum. These fragments differed in size from those present in P. lophurae. These results suggest that the absence of knob protein mRNA in knobless clones is not due to loss of the corresponding gene(s).     

The primary structure of a Plasmodium falciparum polypeptide related to heat shock proteins

A cDNA library constructed from ring-stage RNA isolated from Plasmodium falciparum FCR-3/Gambia was screened with immune human serum and two related positive clones were isolated. Nucleotide sequence analysis of these recombinant clones revealed an open translational reading frame for 681 amino acids with a calculated molecular weight of 74.3 kDa. The deduced amino acid sequence of the polypeptide shows extensive homology to several heat shock proteins (hsp) which have been described. Northern and Southern hybridization analysis indicates that P. falciparum has a second gene which shares common sequences with the hsp gene described in this study.     

Characterization of a beta-tubulin gene and a beta-tubulin gene products of Brugia pahangi

A genomic clone containing a beta-tubulin gene from the parasitic nematode Brugia pahangi was isolated. This gene was sequenced to determine its size, structural organization, and corresponding primary amino acid sequence. The coding sequence of the beta-tubulin gene spans 3.8 kb, is organized into 9 exons and expresses an mNRA of 1.8 kb which codes for a protein of 448 amino acids. The predicted beta-tubulin amino acid sequence is 89%, 94%, 90% and 88% identical to the chicken beta 2, and the Caenorhabditis elegans ben-1, tub-1 and mec-7 gene products, respectively. Southern hybridization analyses demonstrated that there is only one copy of this gene isotype but that other distinct beta-tubulin genes may exist in the Brugia pahangi genome. A nematode specific antipeptide rabbit antiserum raised against the predicted amino acid sequence of the extreme carboxy-terminal region of the B. pahangi beta-tubulin was used to identify beta-tubulin isoforms in adult nematodes and microfilariae. Isoforms detected by this nematode-specific antipeptide antiserum were identical in both adult worms and microfilariae and did not differ from the isoform patterns detected by a monoclonal antibody recognizing a conserved beta-tubulin epitope. This suggests that this carboxy-terminal peptide is highly represented in the beta-tubulin isoforms of B. pahangi.     

Characterisation of the rhoph2 gene of Plasmodium falciparum and Plasmodium yoelii

The high molecular mass protein complex (RhopH) in the rhoptries of the malaria parasite consists of three distinct polypeptides with estimated sizes in Plasmodium falciparum of 155kDa (PfRhopH1), 140kDa (PfRhopH2) and 110kDa (PfRhopH3). Using a number of reagents, including a new mAb 4E10 that is specific for the PfRhopH complex, it was shown that the RhopH complex is synthesised during schizogony and transferred intact to the ring stage in newly invaded erythrocytes. The genes encoding RhopH1 and RhopH3 have already been identified and characterised in both P. falciparum and Plasmodium yoelii. In this report, we describe the identification of the gene for RhopH2 in both these parasite species. Peptide sequences were obtained from purified RhopH2 proteins and used to generate oligonucleotide primers and search malaria sequence databases. In a parallel approach, mAb 4E10 was used to identify a clone coding for RhopH2 from a P. falciparum cDNA library. The sequences of both P. falciparum and P. yoelii genes for RhopH2 were completed and compared. They both contain nine introns and there is a high degree of similarity between the deduced amino acid sequences of the two proteins. The P. falciparum gene is a single copy gene located on chromosome 9, and is transcribed in schizonts.     

Characterization of antigen-expressing Plasmodium falciparum cDNA clones that are reactive with parasite inhibitory antibodies

A Plasmodium falciparum (FCR3 strain) lambda gt11 cDNA expression library was constructed from trophozoite and schizont poly(A) RNA and was screened immunologically with a pooled human immune serum from Nigeria to form a gene bank of 288 positive clones. The gene bank was subsequently screened with parasite inhibitory mouse monoclonal antibodies (mMAb) and with individual human Liberian sera. Two mMAb, 43E5 and 5H10, strongly reacted with 8 and 3 cDNA clones, respectively. Several of those clones also weakly cross-reacted with the other mMAb. Two of those weakly cross-reactive clones, cDNA#366 and cDNA#22, were shown to be located in different chromosomal regions of the parasite by Southern hybridization and so appeared to represent two different parasite genes. The genomic organization of both cDNA#366 and cDNA#22 sequences were identical in the FCR3 and the Honduras-1 strain. The nucleotide sequence of cDNA#366 and the amino acid sequence it coded for were homologous to a partial DNA and amino acid sequence previously reported for a P. falciparum (Camp strain) exoantigen designated p126. The mRNA for cDNA#366 appeared to represent an abundant message in blood stage trophozoites and schizonts.     

Polymorphisms and the differential antiviral activity of the chicken Mx gene

The nucleotide sequence of chicken Mx cDNA was reported earlier using the White Leghorn breed in Germany, but it showed no enhanced resistance to viruses. In this study, the nucleotide sequences of chicken Mx cDNA were determined in many breeds. A total of 25 nucleotide substitutions, of which 14 were deduced to cause amino acid exchanges, were detected, suggesting that the chicken Mx gene is very polymorphic. Transfected cell clones expressing chicken Mx mRNA were established after the Mx cDNA was constructed with an expression vector and introduced into mouse 3T3 cells, and the Mx genes from some breeds were demonstrated to confer positive antiviral responses to influenza virus and vesicular stomatitis virus. On the basis of the comparison among the antiviral activities associated with many Mx variations, a specific amino acid substitution at position 631 (Ser to Asn) was considered to determine the antivirally positive or negative Mx gene. Thus, a single amino acid substitution influences the antiviral activity of Mx in domesticated chickens.     

Isolation of cDNA clones and genomic DNA clones of beta-subunit of chicken prolyl 4-hydroxylase

Prolyl 4-hydroxylase (EC 1.14.11.2) is a key enzyme in collagen biosynthesis. The active enzyme is a tetramer composed of two pairs of non-identical subunits, alpha and beta. Sheep antiserum directed against chicken proly 4-hydroxylase was initially used to screen two cDNA expression libraries. The cDNA was prepared from chicken smooth muscle mRNA and cloned into the plasmids pUC8- and pUC9. Antibodies identified twenty-five clones among the approximately 2 x 10(5) clones in the libraries. Ten clones were isolated pure and used in the subsequent analysis. Monospecific antibodies directed against beta subunit of the enzyme were used in Western-blot analyses of extracts of bacteria carrying the cDNA clones. The results indicated that the clone CPH 9-10B encodes a portion of beta-subunit. The cDNA from CPH 9-10B was used to screen another cDNA library prepared from mRNA from chicken skeletal muscle. Several overlapping clones were isolated. Together the cDNAs correspond to 2.4 kb which is the same as the corresponding mRNA. Three regions of the amino acid sequence deduced from the cDNA sequence matched with that of the NH2-terminus of beta-subunit and two CNBr peptides derived from beta-subunit. The cDNA of CPH 9-10B was also used to screen a genomic DNA library constructed with lambda EMBL-3. Two overlapping genomic clones lambda gCPH beta-22 and beta-50 were isolated and characterized by restriction enzyme analysis. The results indicate that lambda gCPH beta-22 contains the portion of the beta-subunit gene that is transcribed into the 5' portion of beta-subunit mRNA, whereas lambda gCPH beta-50 contains the 3' portion.     

Comparison of the primary structure of the 25 kDa ookinete surface antigens of Plasmodium falciparum and Plasmodium gallinaceum reveal six conserved regions

The gene encoding the 25 kDa ookinete surface antigen (Pgs25) of Plasmodium gallinaceum has been cloned using an oligonucleotide probe directed against one of the EGF-like domains of the P. falciparum 25 kDa ookinete surface antigen (Pfs25). The Pgs25 gene codes for a polypeptide of 215 amino acids, two amino residues less than Pfs25. The deduced amino acid sequence contains a putative signal sequence at the amino-terminus, four tandemly repeated EGF-like domains, and a hydrophobic region at the carboxyl-terminus. By comparing Pgs25 with Pfs25, six conserved regions, consisting of six or more amino acid residues, have been identified. Most of the conserved regions are outside EGF-like core consensus sequences. The most striking conservation is the spacing of the cysteines.     

The polymorphic 11.1 locus of Plasmodium falciparum

Clone pPF11.1 encodes a Plasmodium falciparum antigen expressed during the intraerythrocytic cycle and containing tandem repeats of a 9 amino acid unit. We report here an analysis of the genomic region specific for 11.1, which extends over 30 kb. It contains two blocks of repeats, spanning 13 kb and 9 kb. The restriction map suggests that the locus may result from a gene duplication. The 11.1 region is present in all P. falciparum strains examined so far. Southern analysis of 8 distinct isolates indicates that the locus is highly polymorphic. Thus the pPF11.1 repeats constitute a sensitive and discriminating probe to type P. falciparum strains.