The sequence of a 200 kb portion of a Plasmodium vivax chromosome reveals a high degree of conservation with Plasmodium falciparum chromosome 3

Molecular surveillance of chloroquine resistance in Plasmodium vivax isolates from malaria cases in Yunnan Province of China using pvcrt-o gene polymorphisms

BACKGROUND

The efficacy of chloroquine treatment for vivax malaria has been rarely evaluated due to a lack of an appropriate testing method. The objective of this study was to conduct molecular monitoring of chloroquine resistance in Plasmodium vivax strains from vivax malaria patients in Yunnan Province, focusing on the analysis of polymorphism in the P. vivax chloroquine resistance transporter protein orthologous gene (pvcrt-o).

METHODS

In accordance with the principles of a cohort study, blood samples were collected from malaria cases diagnosed with a P. vivax mono-infection in Yunnan Province from 2020 to 2022. Segmental PCR was used to amplify the whole pvcrt-o gene in the blood samples and their products were subsequently sequenced. The sequencing data were arranged to obtain the full coding DNA sequence (CDS) as well as the gene's promoter region sequences. The CDSs were aligned with the reference sequence (XM_001613407.1) of the P. vivax SalI isolate to identify the mutant loci.

RESULTS

From a total of 375 blood samples taken from vivax malaria cases, 272 both whole gene CDSs (1272-1275 bp) and promoter DNA sequences (707 bp) of pvcrt-o gene were obtained. Among the whole CDSs, there were 7 single nucleotide polymorphic sites in which c.7 A>G was the minor allele frequency (MAF) site with 4.4% (12/272) detection rate. The mutation detection rate showed a significant decrease from 9.8% (10/102) in 2020 to 1.1% (1/92) in 2021 and 1.3% (1/78) in 2022, indicating statistical significance (χ2 = 11.256, P < 0.05). Among the identified 12 haplotypes, the majority of which were wild type (75.7%; 206/272). These four mutant haplotypes (Hap_3, Hap_5, Hap_9, and Hap_10) were classified as "K10 insertion type" and accounted for 12.1% (33/272). The detection rate of Hap_3 increased from 1.0% (1/102) in 2020 to 13.0% (12/92) in 2021 and 14.1% (11/78) in 2022, indicating statistical significance. A total of 23.8% (65/272) of the samples exhibited 14 bp (bp) deletions in the promoter region, occurring most frequently in the wild type haplotype (Hap_1) samples at a rate of 28.6% (59/206).

CONCLUSIONS

In recent years in Yunnan Province, a notable proportion of vivax malaria patients are infected by P. vivax strains with a "K10 insertion" and partial sequence deletions in the promoter region of the pvcrt-o gene, necessitating vigilance.

Single-nucleotide polymorphism, linkage disequilibrium and geographic structure in the malaria parasite Plasmodium vivax: prospects for genome-wide association studies

Background

The ideal malaria parasite populations for initial mapping of genomic regions contributing to phenotypes such as drug resistance and virulence, through genome-wide association studies, are those with high genetic diversity, allowing for numerous informative markers, and rare meiotic recombination, allowing for strong linkage disequilibrium (LD) between markers and phenotype-determining loci. However, levels of genetic diversity and LD in field populations of the major human malaria parasite P. vivax remain little characterized.

Results

We examined single-nucleotide polymorphisms (SNPs) and LD patterns across a 100-kb chromosome segment of P. vivax in 238 field isolates from areas of low to moderate malaria endemicity in South America and Asia, where LD tends to be more extensive than in holoendemic populations, and in two monkey-adapted strains (Salvador-I, from El Salvador, and Belem, from Brazil). We found varying levels of SNP diversity and LD across populations, with the highest diversity and strongest LD in the area of lowest malaria transmission. We found several clusters of contiguous markers with rare meiotic recombination and characterized a relatively conserved haplotype structure among populations, suggesting the existence of recombination hotspots in the genome region analyzed. Both silent and nonsynonymous SNPs revealed substantial between-population differentiation, which accounted for ~40% of the overall genetic diversity observed. Although parasites clustered according to their continental origin, we found evidence for substructure within the Brazilian population of P. vivax. We also explored between-population differentiation patterns revealed by loci putatively affected by natural selection and found marked geographic variation in frequencies of nucleotide substitutions at the pvmdr-1 locus, putatively associated with drug resistance.

Conclusion

These findings support the feasibility of genome-wide association studies in carefully selected populations of P. vivax, using relatively low densities of markers, but underscore the risk of false positives caused by population structure at both local and regional levels.

See commentary: http://www.biomedcentral.com/1741-7007/8/90

An overview of the Babesia, Plasmodium and Theileria genomes: a comparative perspective

Babesia, Plasmodium and Theileria form a triad of apicomplexan hemoparasites and are accountable for significant mortality and morbidity to humans and animals globally. Understanding the pathobiology of these three genera is crucial as multiple drug resistant strains continue to arise in endemic areas along with pesticide and acaricide resistant vector hosts. Vastly improved sequencing technology has produced whole genome sequences of several apicomplexan species and subsequent comparative analyses of these genomes have identified unique as well as common features among the different species, information that will help in the pursuit of alternative therapies, management and perhaps elimination of the disease. This review, therefore, summarizes comparisons of genome structure, protein families, metabolic pathways and organelle biology in these three apicomplexans and how such knowledge has and will continue to enhance the field.

Plasmodium post-genomics: better the bug you know?

Since the publication of the sequence of the genome of Plasmodium falciparum, the major causative agent of human malaria, many post-genomic studies have been completed. Invaluably, these data can now be analysed comparatively owing to the availability of a significant amount of genome-sequence data from several closely related model species of Plasmodium and accompanying global proteome and transcriptome studies. This review summarizes our current knowledge and how this has already been--and will continue to be--exploited in the search for vaccines and drugs against this most significant infectious disease of the tropics.

Gene discovery in Plasmodium vivax through sequencing of ESTs from mixed blood stages

Despite the significance of Plasmodium vivax as the most widespread human malaria parasite and a major public health problem, gene expression in this parasite is poorly understood. To accelerate gene discovery and facilitate the annotation phase of the P. vivax genome project, we have undertaken a transcriptome approach to study gene expression in the mixed blood stages of a P. vivax field isolate. Using a cDNA library constructed from purified blood stages, we have obtained single-pass sequences for approximately 21,500 expressed sequence tags (ESTs), the largest number of transcript tags obtained so far for this species. Cluster analysis revealed that the library is highly redundant, resulting in 5407 clusters. Clustered ESTs were searched against public protein databases for functional annotation, and more than one-third showed a significant match, the majority of these to Plasmodium falciparum proteins. The most abundant clusters were to genes encoding ribosomal proteins and proteins involved in metabolism, consistent with the predominance of trophozoites in the field isolate sample. In spite of the scarcity of other parasite stages in the field isolate, we could identify genes that are expressed in rings, schizonts and gametocytes. This study should facilitate our understanding of the gene expression in P. vivax asexual stages and provide valuable data for gene prediction and annotation of the P. vivax genome sequence.

Identifying and characterising the Plasmodium falciparum merozoite surface protein 10 Plasmodium vivax homologue

Plasmodium vivax malaria is one of the most prevalent parasitic diseases in Asia and Latin-America. The difficulty of maintaining this parasite culture in vitro has hampered identifying and characterising proteins implied in merozoite invasion of red blood cells. We have been able to identify an open reading frame in P. vivax encoding the Plasmodium falciparum merozoite surface protein 10 homologous protein using the partial sequences from this parasite's genome reported during 2004. This new protein contains 479 amino-acids, two epidermal growth factor-like domains, hydrophobic regions at the N- and C-termini, being compatible with a signal peptide and a glycosylphosphatidylinositol anchor site, respectively. The protein is expressed during the parasite's asexual stage and is recognised by polyclonal sera in parasite lysate using Western blot. P. vivax-infected patients' sera highly recognised recombinant protein by ELISA.

The evolution of amino acid repeat arrays in Plasmodium and other organisms

Repeat arrays in protein-coding sequences were analyzed by a novel approach, based on analyzing the distribution of the pairwise proportion of nucleotide differences among units within a repeat array. The results showed that evidence of recent repeat array expansion was particularly characteristic of the repeat arrays of the malaria parasites (genus Plasmodium), supporting the hypothesis that Plasmodium is particularly prone to repeat array expansion by slipped-strand mispairing or a similar mechanism. Repeat arrays in Plasmodium asexual-stage antigens (which are exposed to the immune system of the vertebrate host) had unique characteristics with respect to the number of repeat units, as well as nucleotide and amino acid composition, suggesting that natural selection exerted by the host immune system has shaped features of these arrays.

Variant genes and the spleen in Plasmodium vivax malaria

It is generally accepted that Plasmodium vivax, the most widely distributed human malaria, does not cytoadhere in the deep capillaries of inner organs and thus this malaria parasite must have evolved splenic evasion mechanism in addition to sequestration. The spleen is a uniquely adapted lymphoid organ whose central function is the selective clearance of cell and other particles from the blood, and microbes including malaria. Splenomegaly is a hallmark of malaria and no other disease seems to exacerbate this organ as this disease does. Besides this major selective clearance function however, the spleen is also an erythropoietic organ which, under stress conditions, can be responsible for close to 40% of the RBC populations. Data obtained in experimental infections of human patients with P. vivax showed that anaemia is associated with acute and chronic infections and it has been postulated that the continued parasitemia might have been sufficient to infect and destroy most circulating reticulocytes. We review here the basis of our current knowledge of variant genes in P. vivax and the structure and function of the spleen during malaria. Based on this data, we propose that P. vivax specifically adhere to barrier cells in the human spleen allowing the parasite to escape spleen-clearance while favouring the release of merozoites in an environment where reticulocytes, the predominant, if not exclusive, host cell of P. vivax, are stored before their release into circulation to compensate for the anaemia associated with vivax malaria.

Antibodies against MAEBL ligand domains M1 and M2 inhibit sporozoite development in vitro

MAEBL is a type 1 membrane protein that is implicated in the merozoite invasion of erythrocytes and sporozoite invasion of mosquito salivary glands. This apical organelle protein is structurally similar to the ebl erythrocyte binding proteins, such as EBA-175, except that the tandem ligand domains of MAEBL are similar to part of the extracellular domain of apical membrane antigen 1 and not the Duffy binding-like domain. Although midgut and salivary gland sporozoites are morphologically similar, salivary gland sporozoites undergo a period of new gene expression after infecting the salivary glands, display distinct phenotypic differences, and are more infectious for the mammalian host. The objectives of this project were to determine the molecular form of MAEBL in the infectious salivary gland sporozoites and whether the ligand has a role in the sporozoite development to exoerythrocytic stages in hepatocytes. We determined that MAEBL is newly expressed in salivary gland sporozoites and in a form distinct from what is present in the midgut sporozoites or present in erythrocytic stages. Both ligand domains (M1 and M2) were expressed as part of a full-length membrane form of MAEBL in the salivary gland sporozoites in contrast to the other stages that retain only the M2 ligand domain as part of the membrane form of the protein. Antisera developed against the cysteine-rich regions of the extracellular portion of MAEBL inhibited sporozoite development to exoerythrocytic forms in vitro. Together these data indicate that MAEBL has a role in this third developmental stage in the life cycle of the malaria parasite. Thus, MAEBL is another target for pre-erythrocytic-stage vaccine development against malaria parasites.

Identification of regulatory elements in the Plasmodium falciparum genome

There is little information regarding regulatory sequences in the newly sequenced genome of the malaria parasite, Plasmodium falciparum. Thus, for the first time, a bioinformatic strategy was utilized to identify regulatory elements in this genome using the P. falciparum heat shock protein (hsp) gene family as a model system. Our analysis indicates that the P. falciparum hsp genes do not contain standard eukaryotic regulatory elements. However, a novel G-rich regulatory element named the G-box was identified upstream of several P. falciparum hsp genes and the P. yoelii yoelii, P. berghei, and P. vivax hsp86 genes. Remarkably, the Plasmodium sp. G-boxes were required for maximal reporter gene expression in transient transfection assays. The G-box is not homologous to known eukaryotic elements, and is the best-defined functional element elucidated from Plasmodium sp. Our analysis also revealed several other elements necessary for reporter gene expression including an upstream sequence element, the region surrounding the transcription start site, and the 5' and 3' untranslated regions. These data demonstrate that unique regulatory elements are conserved in the genomes of Plasmodium sp., and demonstrate the feasibility of bioinformatic approaches for their identification.

Genome Sequencing and Comparative Genomics of Tropical Disease Pathogens

The sequencing of eukaryotic genomes has lagged behind sequencing of organisms in the other domains of life, archae and bacteria, primarily due to their greater size and complexity. With recent advances in high-throughput technologies such as robotics and improved computational resources, the number of eukaryotic genome sequencing projects has increased significantly. Among these are a number of sequencing projects of tropical pathogens of medical and veterinary importance, many of which are responsible for causing widespread morbidity and mortality in peoples of developing countries. Uncovering the complete gene complement of these organisms is proving to be of immense value in the development of novel methods of parasite control, such as antiparasitic drugs and vaccines, as well as the development of new diagnostic tools. Combining pathogen genome sequences with the host and vector genome sequences is promising to be a robust method for the identification of host-pathogen interactions. Finally, comparative sequencing of related species, especially of organisms used as model systems in the study of the disease, is beginning to realize its potential in the identification of genes, and the evolutionary forces that shape the genes, that are involved in evasion of the host immune response.

Pilot survey of expressed sequence tags (ESTs) from the asexual blood stages of Plasmodium vivax in human patients

BACKGROUND

Plasmodium vivax is the most widely distributed human malaria, responsible for 70-80 million clinical cases each year and large socio-economical burdens for countries such as Brazil where it is the most prevalent species. Unfortunately, due to the impossibility of growing this parasite in continuous in vitro culture, research on P. vivax remains largely neglected.

METHODS

A pilot survey of expressed sequence tags (ESTs) from the asexual blood stages of P. vivax was performed. To do so, 1,184 clones from a cDNA library constructed with parasites obtained from 10 different human patients in the Brazilian Amazon were sequenced. Sequences were automatedly processed to remove contaminants and low quality reads. A total of 806 sequences with an average length of 586 bp met such criteria and their clustering revealed 666 distinct events. The consensus sequence of each cluster and the unique sequences of the singlets were used in similarity searches against different databases that included P. vivax, Plasmodium falciparum, Plasmodium yoelii, Plasmodium knowlesi, Apicomplexa and the GenBank non-redundant database. An E-value of <10(-30) was used to define a significant database match. ESTs were manually assigned a gene ontology (GO) terminology

RESULTS

A total of 769 ESTs could be assigned a putative identity based upon sequence similarity to known proteins in GenBank. Moreover, 292 ESTs were annotated and a GO terminology was assigned to 164 of them.

CONCLUSION

These are the first ESTs reported for P. vivax and, as such, they represent a valuable resource to assist in the annotation of the P. vivax genome currently being sequenced. Moreover, since the GC-content of the P. vivax genome is strikingly different from that of P. falciparum, these ESTs will help in the validation of gene predictions for P. vivax and to create a gene index of this malaria parasite.

Single-nucleotide polymorphisms and genome diversity in Plasmodium vivax

The study of genetic variation in malaria parasites has practical significance for developing strategies to control the disease. Vaccines based on highly polymorphic antigens may be confounded by allelic restriction of the host immune response. In response to drug pressure, a highly plastic genome may generate resistant mutants more easily than a monomorphic one. Additionally, the study of the distribution of genomic polymorphisms may provide information leading to the identification of genes associated with traits such as parasite development and drug resistance. Indeed, the age and diversity of the human malaria parasite Plasmodium falciparum has been the subject of recent debate, because an ancient parasite with a complex genome is expected to present greater challenges for drug and vaccine development. The genome diversity of the important human pathogen Plasmodium vivax, however, remains essentially unknown. Here we analyze an approximately 100-kb contiguous chromosome segment from five isolates, revealing 191 single-nucleotide polymorphisms (SNPs) and 44 size polymorphisms. The SNPs are not evenly distributed across the segment with blocks of high and low diversity. Whereas the majority (approximately 63%) of the SNPs are in intergenic regions, introns contain significantly less SNPs than intergenic sequences. Polymorphic tandem repeats are abundant and are more uniformly distributed at a frequency of about one polymorphic tandem repeat per 3 kb. These data show that P. vivax has a highly diverse genome, and provide useful information for further understanding the genome diversity of the parasite.

Ten families of variant genes encoded in subtelomeric regions of multiple chromosomes of Plasmodium chabaudi, a malaria species that undergoes antigenic variation in the laboratory mouse

The chromosome ends of human malaria parasites harbour many genes encoding proteins that are exported to the surface of infected red cells, often being involved in host-parasite interactions and immune evasion. Unlike other murine malaria parasites Plasmodium chabaudi undergoes antigenic variation during passage in the laboratory mouse and hence is a model suitable for investigation of switching mechanisms. However, little is known about the subtelomeric regions of P. chabaudi chromosomes and its variable antigens. Here we report 80 kb of sequence from an end of one P. chabaudi chromosome. Hybridization of probes spanning this region to two dimensional pulsed field gels of the genome revealed 10 multicopy gene families located exclusively in subtelomeric regions of multiple P. chabaudi chromosomes, interspersed amongst multicopy intergenic regions. Hence all chromosomes share a common subtelomeric structure, presumably playing a similar role in spatial positioning as the P. falciparum Rep20 sequence. Expression in blood stages, domains characteristic of surface antigens and copy numbers between four and several hundred per genome, indicate a functional role in antigenic variation for some of these families. We identify members of the cir family, as well as novel genes, that although clearly homologous to cir have large low complexity regions in the predicted extracellular domains. Although all families have homologues in other rodent Plasmodium species, four were previously not known to be subtelomeric. Six have homologues in human and simian malarias.

The Plasmodium vivax genome sequencing project

With the successful completion of the project to sequence the Plasmodium falciparum genome, researchers are now turning their attention to other malaria parasite species. Here, an update on the Plasmodium vivax genome sequencing project is presented, as part of the Trends in Parasitology series of reviews expanding on various aspects of P. vivax research.

Low-complexity segments in Plasmodium falciparum proteins are primarily nucleic acid level adaptations

Protein segments that contain few of the possible 20 amino acids, sometimes in tandem repeat arrays, are referred to as containing "simple" or "low-complexity" sequence. Many Plasmodium falciparum proteins are longer than their homologs in other species by virtue of their content of such low-complexity segments that have no known function; these are interspersed among segments of higher complexity to which function can often be ascribed. If there is low complexity at the protein level, there is likely to be low complexity at the corresponding nucleic acid level (departure from equifrequency of the four bases). Thus, low complexity may have been selected primarily at the nucleic acid level and low complexity at the protein level may be secondary. In this case, the amino acid composition of low-complexity segments should be more reflective than that of high complexity segments on forces operating at the nucleic acid level, which include GC-pressure and AG-pressure. Consistent with this, for amino acid determining first and second codon positions, open reading frames containing low-complexity segments show increased contributions to downward GC-pressure (revealed as decreased percentage of G+C) and to upward AG-pressure (revealed as increased percentage A+G). When not countermanded by high contributions to AG-pressure, low-complexity segments can contribute to base order-dependent fold potential; in this respect, they resemble introns. Thus, in P. falciparum, low-complexity segments appear as adaptations primarily serving nucleic acid level functions.

Cytoskeletal proteins with N-terminal signal peptides: plateins in the ciliate Euplotes define a new family of articulins

Protistan cells employ a wide variety of strategies to reinforce and give pattern to their outermost cortical layers. Whereas some use common cytoskeletal elements such as microtubules, others are based on novel cytoskeletal proteins that are as-yet-unknown in higher eukaryotes. The hypotrich ciliate Euplotes possesses a continuous monolayer of scales or plates, located within flattened membranous sacs ('alveoli') just below the plasma membrane, and this provides rigidity and form to the cell. Using immunological techniques, the major proteins comprising these 'alveolar plates' have been identified and termed alpha-, beta-, and gamma-plateins. The present report describes work leading to the molecular characterization of three plateins, alpha 1 and alpha 2 (predicted M(r)s of 61 and 56 kDa) and a beta/gamma form (M(r)=73 kDa). All three proteins have features that are hallmarks of articulins, a class of cytoskeletal proteins that has been identified in the cortex of a wide variety of protistan cells, including certain flagellates, ciliates, dinoflagellates and PLASMODIUM: Chief among these common features are a prominent primary domain of tandem 12-amino acid repeats, rich in valine and proline, and a secondary domain of fewer, shorter repeating units. However, variations in amino acid use within both primary and secondary repetitive domains, and a much more acidic character (predicted pIs of 4.7-4.9), indicate that the plateins represent the first proteins in a new subclass or family of articulins. This conclusion is supported by another novel feature of the plateins, the presence of a canonical hydrophobic signal peptide at the N-terminus of each derived platein sequence. This correlates well with the final cellular location of the plateins, which are assembled into plates within the membrane-limited alveolar sacs. To our knowledge, this is the first report in any eukaryote of cytoskeletal proteins with such start-transfer sequences. Confocal immunofluorescence microscopy, using antibodies to the plateins as probes, reveals that new alveolar plates (enlarging in cortical zones undergoing morphogenesis) label more faintly than mature parental plates. During plate assembly (or polymerization), the plateins thus appear to exist in a more soluble form.

A unique insertion in Plasmodium berghei glucose-6-phosphate dehydrogenase-6-phosphogluconolactonase: evolutionary and functional studies

Plasmodium berghei glucose-6-phosphate dehydrogenase-6-phosphogluconolactonase (G6PD-6PGL) is a bifunctional enzyme with significant sequence similarity in both the 6PGL and G6PD domains to the Plasmodium falciparum enzyme. A recombinant form of the P. berghei enzyme was found to have both G6PD and 6PGL activities, and therefore catalyses the first two steps in the pentose phosphate pathway. Genes encoding very similar proteins are also found in three other malarial parasites, Plasmodium yoelii, Plasmodium chabaudi and Plasmodium knowlesi. All of these predicted enzymes contain unique parasite insertions in corresponding positions in the G6PD domain but the insertions differ in size and sequence. Such insertions are a common feature of malarial proteins but their origin and function is unknown. Excision of the insertion sequence in the P. berghei protein renders the G6PD domain inactive, although the 6PGL activity is unaffected. Replacing the insertion sequence in P. berghei with the insertion sequence from P. falciparum restores some of the G6PD activity and also enhances 6PGL activity. We conclude that although the insertions are evolving rapidly they have an essential role in the activity of the bifunctional enzyme.

Structure of the C-terminal domains of merozoite surface protein-1 from Plasmodium knowlesi reveals a novel histidine binding site

The protozoan parasite Plasmodium causes malaria, with hundreds of millions of cases recorded annually. Protection against malaria infection can be conferred by antibodies against merozoite surface protein (MSP)-1, making it an attractive vaccine candidate. Here we present the structure of the C-terminal domains of MSP-1 (known as MSP-1(19)) from Plasmodium knowlesi. The structure reveals two tightly packed epidermal growth factor-like domains oriented head to tail. In domain 1, the molecule displays a histidine binding site formed primarily by a highly conserved tryptophan. The protein carries a pronounced overall negative charge primarily due to the large number of acidic groups in domain 2. To map protein binding surfaces on MSP-1(19), we have analyzed the crystal contacts in five different crystal environments, revealing that domain 1 is highly preferred in protein-protein interactions. A comparison of MSP-1(19) structures from P. knowlesi, P. cynomolgi, and P. falciparum shows that, although the overall protein folds are similar, the molecules show significant differences in charge distribution. We propose the histidine binding site in domain 1 as a target for inhibitors of protein binding to MSP-1, which might prevent invasion of the merozoite into red blood cells.

Genome sequence and comparative analysis of the model rodent malaria parasite Plasmodium yoelii yoelii

Species of malaria parasite that infect rodents have long been used as models for malaria disease research. Here we report the whole-genome shotgun sequence of one species, Plasmodium yoelii yoelii, and comparative studies with the genome of the human malaria parasite Plasmodium falciparum clone 3D7. A synteny map of 2,212 P. y. yoelii contiguous DNA sequences (contigs) aligned to 14 P. falciparum chromosomes reveals marked conservation of gene synteny within the body of each chromosome. Of about 5,300 P. falciparum genes, more than 3,300 P. y. yoelii orthologues of predominantly metabolic function were identified. Over 800 copies of a variant antigen gene located in subtelomeric regions were found. This is the first genome sequence of a model eukaryotic parasite, and it provides insight into the use of such systems in the modelling of Plasmodium biology and disease.

Prediction of many new exons and introns in Plasmodium falciparum chromosome 2

The current prediction of genes in the Plasmodium falciparum genome database relies upon a limited number of specially developed computer algorithms. We have re-annotated the sequence of chromosome 2 of P. falciparum by a computer-assisted manual analysis, which is described here. Of 161 newly predicted introns, we have experimentally confirmed 98. We regard 110 introns from the previously published analyses as probable, we delete 3, change 26 and add 135. We recognise 214 genes in chromosome 2. We have predicted introns in 121 genes. The increased complexity of gene structure on chromosome 2 is likely to be mirrored by the entire genome.