Plasmodium vivax dhfr mutations among isolates from malarious areas of Iran

The use of sulfadoxine and pyrimethamine (SP) for treatment of vivax malaria is uncommon in most malarious areas, but Plasmodium vivax isolates are exposed to SP because of mixed infections with other Plasmodium species. As P. vivax is the most prevalent species of human malaria parasites in Iran, monitoring of resistance of the parasite against the drug is necessary. In the present study, 50 blood samples of symptomatic patients were collected from 4 separated geographical regions of south-east Iran. Point mutations at residues 57, 58, 61, and 117 were detected by the PCR-RFLP method. Polymorphism at positions 58R, 117N, and 117T of P. vivax dihydrofolate reductase (Pvdhfr) gene has been found in 12%, 34%, and 2% of isolates, respectively. Mutation at residues F57 and T61 was not detected. Five distinct haplotypes of the Pvdhfr gene were demonstrated. The 2 most prevalent haplotypes were F57S58T61S117 (62%) and F57S58T61N117 (24%). Haplotypes with 3 and 4 point mutations were not found. The present study suggested that P. vivax in Iran is under the pressure of SP and the sensitivity level of the parasite to SP is diminishing and this fact must be considered in development of malaria control programs.     

Plasmodium vivax: Prevalence of mutations associated with sulfadoxine–pyrimethamine resistance in Plasmodium vivax clinical isolates from Pakistan

The main aim of the present study was to investigate the frequency of SNPs-haplotypes of dhfr and dhps genes associated to sulfadoxine–pyrimethamine (SP) resistance in Plasmodium vivax clinical isolates circulating in a malaria endemic area, Pakistan. All 164 collected isolates were analyzed for SNPs-haplotypes at positions 13, 33, 57, 58, 61, 117 and 173 of pvdhfr and 383 and 553 of pvdhps genes using PCR–RFLP methods. All examined isolates were found to carry wild-type amino acids at positions 13, 33, 57, 61 and 173, while 58R and 117N mutations were detected among 15.2% and 53.6% of isolates, respectively. Based on the size polymorphism of pvdhfr genes at repeat region, type B (79.3%) was the most prevalent variant. The combination of pvdhfr and pvdhps haplotypes demonstrated nine distinct haplotypes. The three most prevalent haplotypes were I₁₃P₃₃F₅₇S₅₈T₆₁S₁₁₇I₁₇₃/A₃₈₃A₅₅₃ (43.9%), I₁₃P₃₃F₅₇S₅₈T₆₁N₁₁₇I₁₇₃/A₃₈₃A₅₅₃ (33.6%) and I₁₃P₃₃F₅₇R₅₈T₆₁N₁₁₇I₁₇₃/A₃₈₃A₅₅₃ (12.2%). The presence of mutant haplotypes is worrying and indicates the emergence of drug tolerant/resistant P. vivax isolates in Pakistan in near future.     

Genetic Polymorphisms in Plasmodium vivax Dihydrofolate Reductase and Dihydropteroate Synthase in Isolates from the Philippines,Bangladesh, and Nepal

Genetic polymorphisms of pvdhfr and pvdhps genes of Plasmodium vivax were investigated in 83 blood samples collected from patients in the Philippines, Bangladesh, and Nepal. The SNP-haplotypes of the pvdhfr gene at the amino acid positions 13, 33, 57, 58, 61, 117, and 173, and that of the pvdhps gene at the positions 383 and 553 were analyzed by nested PCR-RFLP. Results suggest diverse polymorphic patterns of pvdhfr alone as well as the combination patterns with pvdhps mutant alleles in P. vivax isolates collected from the 3 endemic countries in Asia. All samples carried mutant combination alleles of pvdhfr and pvdhps. The most prevalent combination alleles found in samples from the Philippines and Bangladesh were triple mutant pvdhfr combined with single mutant pvdhps allele and triple mutant pvdhfr combined with double wild-type pvdhps alleles, respectively. Those collected from Nepal were quadruple mutant pvdhfr combined with double wild-type pvdhps alleles. New alternative antifolate drugs which are effective against sulfadoxine-pyrimethamine (SP)-resistant P. vivax are required.     

To what extent can traditional medicine contribute a complementary or alternative solution to malaria control programmes?

Background

Sulphadoxine and pyrimethamine are anti-folate drugs that show synergistic anti-malarial effect. Point mutations in dihydrofolate reductase (dhfr) and dihydropteorate synthatase (dhps) cause anti-folate drug resistance phenotype in human malaria parasites. This study presents pattern of point mutations in dhfr/dhps genes among Indian sub-continent.

Methods

Microscopically diagnosed one hundred Plasmodium vivax field isolates were collected from five widely separated geographical regions of India. Dhfr and dhps genes were PCR amplified and sequenced. Previously published mutations data were collected and analyzed using Chi square test to identify geographical cluster of mutant/wild type genotypes.

Results

Sequence analysis revealed single (S58R), double (S58R/S117N) and quadruple (F57L/S58R/T61M/S117T/) point mutations at dhfr and single (A383G) to double (A383G/A553G) mutations at dhps in P. vivax field isolates. In addition, three new mutations were also observed at dhfr. Both, dhfr and dhps genes revealed tandem repeat variations in field isolates. Dhps revealed very low mutation frequency (14.0%) compared to dhfr (50.70%). Comparative analysis revealed a progressive increase in frequency of quadruple mutant dhfr genotype (p < 0.001) within five years in north-eastern state (Kamrup, Assam). Frequency of dhfr genotypes revealed three distinct geographical clusters of wild (northern India), double mutant (southern India), and quadruple mutant (north-eastern and island regions of India) on the Indian sub-continent.

Conclusion

Study suggests that SP may be susceptible to P. vivax in India, except Andaman and north-eastern state. The distinction of geographical regions with sensitive and resistant parasite phenotypes would be highly useful for designing and administering national anti-malarial drug policy.     

Differentiation, multiplication and control of bloodstream form Trypanosoma (Duttonella) vivax in mice

The growth and differentiation of Trypanosoma vivax was studied in intact and irradiated C3H/He and C57Bl/6 mice. In irradiated (800 R) or intact C3H/He and irradiated (800 R) C57Bl/6 mice, T. vivax parasitaemia increased rapidly then entered a plateau phase and thereafter declined in an antibody-independent remission phase. Throughout the infection, variations were observed in parasite morphology, density, DNA content, number of organisms with 2 nuclei and 2 kinetoplasts and infectivity of parasites for mice. Parasites in exponential phase had the highest number of members in the S, G2 and M phases of the cell cycle as determined by staining with the interchalating dye Chromomycin A3 and analysis on a flow cytometer. During this phase there were numerous parasites with 2 nuclei and 2 kinetoplasts and infectivity was high for mice. As the parasitaemia approached and entered the plateau phase, the proportion of organisms in the S, G2 and M phases of the cell cycle as well as the number of those with 2 kinetoplasts decreased slightly; the number of organisms with 2 nuclei decreased rapidly; and parasites had a considerably reduced capacity to infect mice. Organisms from the remission phase contained only 1 nucleus and 1 kinetoplast and were not infective for mice. The study suggests that T. vivax organisms transit from dividing to committed non-dividing forms and that some non-diving, non-infective T. vivax organisms remain trapped in the S, G2 and M stages of the cell cycle and die without completing binary fission.(ABSTRACT TRUNCATED AT 250 WORDS)     

Analysis and classification of 304 mutant alleles in patients with type 1 and type 3 Gaucher disease

Gaucher disease results from the inherited deficiency of the enzyme glucocerebrosidase (EC 3.2.1.45). Although >100 mutations in the gene for human glucocerebrosidase have been described, most genotype-phenotype studies have focused upon screening for a few common mutations. In this study, we used several approaches-including direct sequencing, Southern blotting, long-template PCR, restriction digestions, and the amplification refraction mutation system (ARMS)-to genotype 128 patients with type 1 Gaucher disease (64 of Ashkenazi Jewish ancestry and 64 of non-Jewish extraction) and 24 patients with type 3 Gaucher disease. More than 97% of the mutant alleles were identified. Fourteen novel mutations (A90T, N117D, T134I, Y135X, R170C, W184R, A190T, Y304X, A341T, D399Y, c.153-154insTACAGC, c.203-204insC, c.222-224delTAC, and c.1122-1123insTG) and many rare mutations were detected. Recombinant alleles were found in 19% of the patients. Although 93% of the mutant alleles in our Ashkenazi Jewish type 1 patients were N370S, c.84-85insG, IVS2+1G-->A or L444P, these four mutations accounted for only 49% of mutant alleles in the non-Jewish type 1 patients. Genotype-phenotype correlations were attempted. Homozygosity or heterozygosity for N370S resulted in type 1 Gaucher disease, whereas homozygosity for L444P was associated with type 3. Genotype L444P/recombinant allele resulted in type 2 Gaucher disease, and homozygosity for a recombinant allele was associated with perinatal lethal disease. The phenotypic consequences of other mutations, particularly R463C, were more inconsistent. Our results demonstrate a high rate of mutation detection, a large number of novel and rare mutations, and an accurate assessment of the prevalence of recombinant alleles. Although some genotype-phenotype correlations do exist, other genetic and environmental factors must also contribute to the phenotypes encountered, and we caution against relying solely upon genotype for prognostic or therapeutic judgements.     

Determining the frequency of common mutations in the GBA gene in patients with Gaucher disease in Ukraine

A molecular-genetics investigation is conducted on 27 patients from 26 families. Common mutations in the GBA gene (N370S, L444P, and 84GG) are studied. The overall frequency of the common mutations is nearly 58%, with the percentage of alleles that carry the N370S mutation close to 42.3% and the proportion that carry the L444P mutation, 15.4%. No allele containing the 84GG mutation was found. Besides other mutations, the rare mutations P178S, W184R, and Rec Nci I (together with N370S) were also found in the GBA gene in patients with the nonneuronopathic form of the disease, along with the genotypes G377S/c 999GA and D409H/R 120W/G202R in patients with the chronic neuronopathic form. An analysis of the correlation between the genotype and the course of the disease in the patients showed that the genotype-phenotype correlations were close to that described for European populations.     

Functional consequences of PRODH missense mutations

PRODH maps to 22q11 in the region deleted in the velocardiofacial syndrome/DiGeorge syndrome (VCFS/DGS) and encodes proline oxidase (POX), a mitochondrial inner-membrane enzyme that catalyzes the first step in the proline degradation pathway. At least 16 PRODH missense mutations have been identified in studies of type I hyperprolinemia (HPI) and schizophrenia, 10 of which are present at polymorphic frequencies. The functional consequences of these missense mutations have been inferred by evolutionary conservation, but none have been tested directly. Here, we report the effects of these mutations on POX activity. We find that four alleles (R185Q, L289M, A455S, and A472T) result in mild (<30%), six (Q19P, A167V, R185W, D426N, V427M, and R431H) in moderate (30%-70%), and five (P406L, L441P, R453C, T466M, and Q521E) in severe (>70%) reduction in POX activity, whereas one (Q521R) increases POX activity. The POX encoded by one severe allele (T466M) shows in vitro responsiveness to high cofactor (flavin adenine dinucleotide) concentrations. Although there is limited information on plasma proline levels in individuals of known PRODH genotype, extant data suggest that severe hyperprolinemia (>800 microM) occurs in individuals with large deletions and/or PRODH missense mutations with the most-severe effect on function (L441P and R453C), whereas modest hyperprolinemia (300-500 microM) is associated with PRODH alleles with a moderate reduction in activity. Interestingly, three of the four alleles associated with or found in schizophrenia (V427M, L441P, and R453C) resulted in severe reduction of POX activity and hyperprolinemia. These observations plus the high degree of polymorphism at the PRODH locus are consistent with the hypothesis that reduction in POX function is a risk factor for schizophrenia.     

Genetic polymorphisms and haplotypes of the organic cation transporter 1 gene (SLC22A1) in the Xhosa population of South Africa

Human organic cation transporter 1 is primarily expressed in hepatocytes and mediates the electrogenic transport of various endogenous and exogenous compounds, including clinically important drugs. Genetic polymorphisms in the gene coding for human organic cation transporter 1, SLC22A1, are increasingly being recognized as a possible mechanism explaining the variable response to clinical drugs, which are substrates for this transporter. The genotypic and allelic distributions of 19 nonsynonymous and one intronic SLC22A1 single nucleotide polymorphisms were determined in 148 healthy Xhosa participants from South Africa, using a SNAPshot^® multiplex assay. In addition, haplotype structure for SLC22A1 was inferred from the genotypic data. The minor allele frequencies for S14F (rs34447885), P341L (rs2282143), V519F (rs78899680), and the intronic variant rs622342 were 1.7%, 8.4%, 3.0%, and 21.6%, respectively. None of the participants carried the variant allele for R61C (rs12208357), C88R (rs55918055), S189L (rs34104736), G220V (rs36103319), P283L (rs4646277), R287G (rs4646278), G401S (rs34130495), M440I (rs35956182), or G465R (rs34059508). In addition, no variant alleles were observed for A306T (COSM164365), A413V (rs144322387), M420V (rs142448543), I421F (rs139512541), C436F (rs139512541), V501E (rs143175763), or I542V (rs137928512) in the population. Eight haplotypes were inferred from the genotypic data. This study reports important genetic data that could be useful for future pharmacogenetic studies of drug transporters in the indigenous Sub-Saharan African populations.     

Functional characterization of genetic variants of human FMO3 associated with trimethylaminuria

Impaired conversion of trimethylamine to trimethylamine N-oxide by human flavin containing monooxygenase 3 (FMO3) is strongly associated with primary trimethylaminuria, also known as 'fish-odor' syndrome. Numerous non-synonymous mutations in FMO3 have been identified in patients suffering from this metabolic disorder (e.g., N61S, M66I, P153L, and R492W), but the molecular mechanism(s) underlying the functional deficit attributed to these alleles has not been elucidated. The purpose of the present study was to determine the impact of these disease-associated genetic variants on FMO3 holoenzyme formation and on steady-state kinetic parameters for metabolism of several substrates, including trimethylamine. For comparative purposes, several common allelic variants not associated with primary trimethylaminuria (i.e., E158K, V257M, E308G, and the E158K/E308G haplotype) were also analyzed. When recombinantly expressed in insect cells, only the M66I and R492W mutants failed to incorporate/retain the FAD cofactor. Of the remaining mutant proteins P153L and N61S displayed substantially reduced (<10%) catalytic efficiencies for trimethylamine N-oxygenation relative to the wild-type enzyme. For N61S, reduced catalytic efficiency was solely a consequence of an increased K(m), whereas for P153L, both K(m) and k(cat) were altered. Similar results were obtained when benzydamine N-oxygenation was monitored. A homology model for FMO3 was constructed based on the crystal structure for yeast FMO which places the N61 residue alone, of the mutants analyzed here, in close proximity to the FAD catalytic center. These data demonstrate that primary trimethylaminuria is multifactorial in origin in that enzyme dysfunction can result from kinetic incompetencies as well as impaired assembly of holoprotein.     

Sequence polymorphisms in Pvs48/45 and Pvs47 gametocyte and gamete surface proteins in Plasmodium vivax isolated in Korea

Nucleotide sequence analyses of the Pvs48/45 and Pvs47 genes were conducted in 46 malaria patients from the Republic of Korea (ROK) (n = 40) and returning travellers from India (n = 3) and Indonesia (n = 3). The domain structures, which were based on cysteine residue position and secondary protein structure, were similar between Plasmodium vivax (Pvs48/45 and Pvs47) and Plasmodium falciparum (Pfs48/45 and Pfs47). In comparison to the Sal-1 reference strain (Pvs48/45, PVX_083235 and Pvs47, PVX_083240), Korean isolates revealed seven polymorphisms (E35K, H211N, K250N, D335Y, A376T, I380T and K418R) in Pvs48/45. These isolates could be divided into five haplotypes with the two major types having frequencies of 47.5% and 20%, respectivelfy. In Pvs47, 10 polymorphisms (F22L, F24L, K27E, D31N, V230I, M233I, E240D, I262T, I273M and A373V) were found and they could be divided into four haplotypes with one major type having a frequency of 75%. The Pvs48/45 isolates from India showed a unique amino acid substitution site (K26R). Compared to the Sal-1 and ROK isolates, the Pvs47 isolates from travellers returning from India and Indonesia had amino acid substitutions (S57T and I262K). The current data may contribute to the development of the malaria transmission-blocking vaccine in future clinical trials.     

Detection of the frequencies of GBA gene major mutations in patients with Gaucher disease in Ukraine

The molecular diagnostics of 27 from 26 Ukrainian families has been performed. The common mutations in GBA gene (N370S, L444P and 84GG) accounted for up to 58% of all cases: mutation N370S was detected in 42.3% alleles, mutation L444P was observed in 15.4% alleles and mutation 84GG was not found at all. The other mutations were: P178S, W184R and Rec Nci I (in compounds with N370S) in the patients with nonneuronopathic form of Gaucher disease, and the genotypes G377S/c 999G --> A and D409H/R120W/G202R were detected in patients with chronic neuronopathic form of Gaucher disease. The data analysis of the genotype and disease progression in the patients allows confirming the known genotype-phenotype correlation.     

Prevalence of GJB2 (CX26) gene mutations in south Iranian patients with autosomal recessive nonsyndromic sensorineural hearing loss

Hereditary hearing loss is a genetically heterogeneous disorder. Mutations in connexin 26 (CX26), are a major cause in many countries and are largely dependent on ethnic groups. The purpose of our study was to evaluate the prevalence of GJB2 mutations among affected individuals from south of Iran. Fifty patients presenting with autosomal recessive non-syndromic hearing loss from Fars, province in south of Iran, were studied for mutations in GJB2 gene and screened by direct sequencing. Mutations were detected in 15 out of 50 patients (30?%). Eight different mutations were identified; six of them were previously identified (35delG, V27I M34V, V153I, A149T, V198M). The remaining two alleles, L28I and N169T, were novel variants. The most common mutations were 35delG followed by V153I with an allele frequency of 7 and 6?%, respectively. In this study, 30?% of our subjects were found to have the causative variants or polymorphisms in GJB2 and the c.35delG mutation was the most common cause in our patients. However, more study with larger sample size as well as in vitro functional study for these new variants in Xenopus oocytes is required.     

Natural Selection Mediated Association of the Duffy (FY) Gene Polymorphisms with Plasmodium vivax Malaria in India

The Duffy (Fy) antigens act as receptors for chemokines as well as for Plasmodium vivax to invade human RBCs. A recent study has correlated the occurrence of the FY*A allele of Duffy gene with decreased susceptibility to vivax malaria, but no epidemiological correlation between the distribution of FY*A allele and incidences of vivax malaria has been established so far. Furthermore, if such correlations exist, whether natural selection has mediated the association, is an important question. Since India is highly endemic to P. vivax malaria with variable eco-climatic and varying vivax malaria epidemiology across different regions, such a question could well be answered in Indians. For this, we have genotyped the FY gene at the −33^rd and the 125^th nucleotide positions in 250 Indians sampled from six different zonal plus one tribal population covering the whole of India and studied possible correlations with eco-climatic and vivax malaria incidences. No FY*O allele was found, however, both the FY*A and FY*B alleles forming FY*A/FY*A, FY*A/FY*B and FY*B/FY*B genotypes were widely distributed among Indians. Five out of seven population samples significantly deviated from the Hardy-Weinberg equilibrium expectation, and two alleles (FY*A and FY*B) and the homozygote genotype, FY*B/FY*B were clinally distributed over the population coordinates. Furthermore, vivax malaria incidences over the past five years were significantly negatively and positively associated with the frequencies of the FY*A and FY*B alleles, respectively. The Northern Indians were highly differentiated from the other zonal population samples at the FY gene, as evidenced from the reconstructed Neighbor-Joining phylogenetic tree. The results specify the role of natural selection in the distribution of FY gene polymorphism in India. Furthermore, the hypotheses on the part of the FY*A allele in conferring protection to vivax malaria could be validated following population genetic studies in a vivax malaria epidemiological setting, such as India.     

The baseline distribution of malaria in the initial phase of elimination in Sabang Municipality, Aceh Province, Indonesia

ABSTRACT: BACKGROUND: Sabang Municipality, in Aceh Province, Indonesia, plans to initiate a malaria elimination programme in 2013. A baseline survey of the distribution of malaria in the municipality was conducted to lay the foundations for an evidence-based programme and to assess the island's readiness to begin the elimination process. METHODS: The entire population of the municipality was screened for malaria infection and G6PD deficiency. Specimens collected included blood slides, blots and tubes for selected households. Results and Discussion Samples were collected from 16,229 residents. Microscopic examination of the blood smears revealed 12 malaria infections; 10 with Plasmodium falciparum and 2 with Plasmodium vivax. To confirm the parasite prevalence, polymerase chain reaction (PCR) diagnosis was performed on the entire positive cases by microscopy and randomized 10% of the microscopically negative blood samples. PCR revealed an additional 11 subjects with malaria; one P. falciparum infection from the village of Paya Keunekai, and nine P. vivax infections and one mixed P. falciparum/P. vivax infection from the village of Batee Shok. The overall slide positivity rate was 0.074% (CI 95%: 0.070 - 0.078) and PCR corrected prevalence 0,590% (CI 95%: 0.582 - 0.597). Analysis of 937 blood samples for G6PD deficiency revealed two subjects (0.2%) of deficient G6PD. Analysis of several genes of the parasite, such as Pfdhfr, Pfdhps, Pfmdr1, Pfcrt, Pfmsp1, Pfmsp2, Pvdhfr, Pvdhps, Pvmdr1 and host gene, such as G6PD gene revealed that both P. falciparum and P. vivax carried the mutation associated with chloroquine resistance. CONCLUSION: Malariometric and host genetic analysis indicated that there is a low prevalence of both malaria and G6PD deficiency in the population of Sabang Municipality. Nevertheless, malaria cases were clustered in three rural villages and efforts for malaria elimination in Sabang should be particularly focused on those three villages.     

Trypanosoma (Duttonefla) vivax

Although Trypanosoma vivax was first discovered in 1905 (Ref. 1), the fact that most stocks of this parasite are restricted to ruminant hosts has retarded investigation of this species compared with the experimentally more amenable T. brucei and T. congolense. The veterinary importance of T. vivax (Box 1) and a recent report suggesting that T. vivax may have an even more extended range than previously thought (Box 2) prompts an evaluation of the current knowledge of the biology of this trypanosome.     

Melanocortin 1-receptor (MC1R) mutations are associated with plumage colour in chicken

The co-segregation of plumage colour and sequence polymorphism in the melanocortin 1-receptor gene (MC1R) was investigated using an intercross between the red junglefowl and White Leghorn chickens. The results provided compelling evidence that the Extended black (E) locus controlling plumage colour is equivalent to MC1R. E/MC1R was assigned to chromosome 11 with overwhelming statistical support. Sequence analysis indicated that the E92K substitution, causing a constitutively active receptor in the sombre mouse, is the most likely causative mutation for the Extended black allele carried by the White Leghorn founders in this intercross. The MC1R sequence associated with the recessive buttercup (ebc) allele indicated that this allele evolved from a dominant Extended black allele as it shared the E92K and M71T substitutions with some E alleles. It also carried a third missense mutation H215P which thus may interfere with the constitutive activation of the receptor caused by E92K (and possibly M71T).     

Frequencies of cystic fibrosis mutations in the Maine population: high proportion of unknown alleles in individuals of French-Canadian ancestry

Cystic fibrosis (CF) is one of the most common severe autosomal recessive disorders in Caucasian populations. A mutation in the cystic fibrosis transmembrane conductance regulator (CFTR) gene causes this disorder. Reported here is the first analysis of CF mutations in the Maine population. We have screened 263 CF chromosomes for 16 previously reported mutations. Analysis of DNA from 124 apparently unrelated CF patients and 15 obligate carrier parents (whose partner and affected child were unavailable for study) resulted in the identification of 91% of the CF alleles and complete genotyping of 85% of the patients. The frequencies (%) of these mutations in the Maine population are ΔF508 (75% of the chromosomes), G85E (0.76), R117H (0.76), I148T (1.1), 621+1G→T (1.1), 711+1G→T (3.0), A455E (1.1), 1717-1G→A (1.1), G542X (1.9), G551D (1.9), R560T (0.76), Y1092X (0.38), W1282X (0.38), and N1303K (1.5). The exon 10 mutation, ΔI507, and the exon 11 mutation, R553X, were not observed. Surprisingly, whereas only 5% of the alleles remain unidentified in the non-French population, the unidentified proportion in the French population is 19%. CF testing for the Maine population will be further improved as the as yet unidentified CF mutations in this population are characterized. Received: 17 January 1996 / Revised: 28 February 1996     

Characterization of an allele-nonspecific intragenic suppressor in the yeast plasma membrane H+-ATPase gene (Pma1).

We have analyzed the ability of A165V, V169I/D170N, and P536L mutations to suppress pma1 dominant lethal alleles and found that the P536L mutation is able to suppress the dominant lethality of the pma1-R271T, -D378N, -D378E, and -K474R mutant alleles. Genetic and biochemical analyses of site-directed mutants at Pro-536 suggest that this amino acid may not be essential for function but is important for biogenesis of the ATPase. Proteins encoded by dominant lethal pma1 alleles are retained in the endoplasmic reticulum, thus interfering with transport of wild-type Pma1. Immunofluorescence studies of yeast conditionally expressing revertant alleles show that the mutant enzymes are correctly located at the plasma membrane and do not disturb targeting of the wild-type enzyme. We propose that changes in Pro-536 may influence the folding of the protein encoded by a dominant negative allele so that it is no longer recognized and retained as a misfolded protein by the endoplasmic reticulum.