Reversible inactivation of a foreign gene, hph, during the asexual cycle in Neurospora crassa transformants

Summary A plasmid construct carrying the hygromycin phosphotransferase (hph) gene fused to the expression elements of the trpC gene of Aspergillus nidulans was used to obtain hygromycin B (Hyg)-resistant transformants of Neurospora crassa. The plasmid does not have any homology with the N. crassa genome. Here we demonstrate that most of the transformants arise from integration of the transforming DNA into only one of the nuclei present in the protoplasts. Furthermore, in most of the transformants the integrated transforming DNA is physically stable after growth of the transformants for about 25 nuclear divisions without Hyg selection, in spite of being present in multiple copies. In transformants carrying only a single insertion, phenotypic expression of the hph gene remains unaltered in conidial isolates obtained withoug Hyg selection. On the other hand, about 40% of transformants harbouring plasmid DNA integrated at more than one location yield conidial isolates showing reversible inactivation of the hph genes. Interestingly, the presence of methylated cytosine residues in the integrated DNA is strongly correlated with the number of plasmid copies. The hph genes are heavily methylated in transformants harbouring multiple copies but not in those harbouring only one copy of the plasmid. Phenotypic expression of the inactive hph genes can be restored by growing the transformants either under Hyg selection pressure or in the presence of 5-azacytidine. In the first case the hph genes are again inactivated when Hyg selection pressure is removed, while the activation of the hph gene by 5-azacytidine gives stable Hyg^r strains.Dedicated to Dr. T.A. Trautner on the occasion of his 60^th birthday     

Analysis of sorbose resistance in Neurospora crassa in heterokaryons of sorbose resistant mutants; contribution to the genetics of active transport

Summary Suitable auxotrophic markers were introduced into sorbose-resistant mutants and the sorbose-sensitive wildtype strain. Pairwise combinations of one resistant and one sensitive strain each as well as of two sensitive strains were then grown on minimal-agar to obtain forced heterocaryons. The growth behaviour of these on minimal-agar with and without added sorbose was compared.Of seven resistant mutants, representing six separate genes, among which were genes A and B, six mutants were recessive to the wildtype. The seventh, representing gene C, was recessive only with regard to colony-size, but intermediate with regard to germination counts. Heterocaryons forced between pairs of 2 closely linked mutants (intragenic case of the type A^– ₁+A^– ₂) were resistant, as were the separate mutants. However two heterocaryons forced between pairs of unlinked mutants (intergenic case of the type A^–+B^–) were sorbose sensitive. Heterocaryons forced between A or B-mutants and the C-mutant mentioned, unlinked to either A or B (intergenic cases of the type A^–+C^– and B^–+C^–) were more sensitive than the separate mutants but more resistant than the wildtype.It follows that sorbose-resistant mutants in heterocaryons of the intergenic types can complement each others defects (no growth complementation), but can not do so in heterocaryons of the intragenic type. Their complementation is considered to be the result of the activity of the intact wildtype genes homologous to the defective ones that are contained together in the multinucleate cells of the heterocaryons. This complementation may be taken as evidence for the recessiveness resp. intermediate expression of the different resistant mutants.Since none of the mutants checked so far were dominant compared to the wildtype, none of them can be a regulator-mutant. The possibility of explaining them as suppressor mutants is restricted by their recessiveness to mechanisms of suppression giving a recessive phenotype. An alternative explanation suggests that the respective wildtype genes may contain structural information for the synthesis of permeases involved in sorbose transport. The mutants would then be resistant due to defective permeases. Their recessiveness is in full accord with this suggestion.

---

---

II. Teil einer Habilitationsschrift bei der Naturwissenschaftlichen Fakultät der Universität München.     

Calmodulin defects cause the loss of Ca2+-dependent K+ currents in two pantophobiac mutants ofParamecium tetraurelia

Summary Two behavioral mutants ofParamecium tetraurelia, pantophobiacs A¹ and A², have single amino acid defects in the structure of calmodulin. The mutants exhibit several major ion current defects under voltage clamp: (i) the Ca²⁺-dependent K⁺ current activated upon depolarization ofParamecium is greatly reduced or missing in both mutants, (ii) both mutants lack a Ca²⁺-dependent K⁺ current activated upon hyperpolarization, and (iii) the Ca²⁺-dependent Na⁺ current is significantly smaller in pantophobiac A¹ compared with the wild type, whereas this current is slightly increased in pantophobiac A².Other, minor defects include a reduction in peak amplitude of the depolarization-activated Ca²⁺ current in pantophobiac A², increased rates of voltage-dependent inactivation of this Ca²⁺ current in both pantophobiac A¹ and pantophobiac A², and an increase in the time required for the hyperpolarization-activated Ca²⁺ current to recover from inactivation in the pantophobiacs.The diversity of the pantophobiac mutations' effects on ion current function may indicate specific associations of calmodulin with a variety of Ca²⁺-related ion channel species inParamecium.     

Growth of catalase A and catalase T deficient mutant strains of Saccharomyces cerevisiae on ethanol and oleic acid

The parental strain (A⁺T⁺) of Saccharomyces cerevisiae and mutants, deficient in catalase T (A⁺T^–), catalase A (A^–T⁺) or both catalases (A^–T^–), grew on ethanol and oleic acid with comparable doubling times. Specific activities of catalase were low in glucose- and ethanol-grown cells. In the two oleic acid-grown A⁺-strains (A⁺T⁺ and A⁺T^–) high catalase activities were found; catalase activity invariably remained low in the A^–T⁺ strain and was never detected in the A^–T^– strain. The levels of -oxidation enzymes in oleic acid-grown cells of the parental and all mutant strains were not significantly different. However, cytochrome C peroxidase activity had increased 8-fold in oleic acid grown A^– strains (A^–T⁺ and A^–T^–) compared to parental strain cells. The degree of peroxisomal proliferation was comparable among the different strains. Catalase A was shown to be located in peroxisomes. Catalase T is most probably cytosolic in nature and/or present in the periplasmic space.     

Genetic,biochemical and immunological evidence for the involvement of two alcohol dehydrogenases in the metabolism of propane by Rhodococcus rhodochrous PNKb1

NAD⁺-dependent propan-1-ol and propan-2-ol dehydrogenase activities were detected in cell-free extracts of Rhodococcus rhodochrous PNKb1 grown on propane and potential intermediates of propane oxidation. However, it was unclear whether this activity was mediated by one or more enzymes. The isolation of mutants unable to utilize propan-1-ol (alcA^-) or propan-2-ol (alcB^-) as sole carbon and energy sources demonstrated that these substrates are metabolized by different alcohol dehydrogenases. These mutants were also unable to utilize propane as a growth substrate indicating that both alcohols are intermediates of propane metabolism. Therefore, propane is metabolized by terminal and sub-terminal oxidation pathways. Westernblot analysis demonstrated that a previously purified NAD⁺-dependent propan-2-ol dehydrogenase (Ashraf and Murrell 1990) was only synthesized after growth on propane and sub-terminal oxidation intermediates (but not acetone), and not propan-1-ol or terminal oxidation intermediates. Therefore, our evidence suggest that another dehydrogenase is involved in the metabolism of propan-1-ol and this agrees with the isolation of the alcA^- and alcB^- phenotypes. The previously characterized NAD⁺-dependent propan-2-ol dehydrogenase from R. rhodochrous PNKb1 is highly conserved amongst members of the propane-utilizing Rhodococcus-Nocardia complex.     

Extra divisions and nuclei fusions in microspores from Brassica allohexaploid (AABBCC) × Orychophragmus violaceus hybrids

Abnormal meiosis and microspore development and related defective mutants have often been reported in plants and wide hybrids. Here extra divisions and nuclei fusions were observed to occur in microspore nuclei of partial hybrids between synthetic Brassica hexaploid (2n=54, AABBCC) and another crucifer Orychophragmus violaceus (2n=24). Abnormal spindle were formed and chromosomes were separated into several nuclei of variable sizes after bi-, or multi-polar divisions in the four cells of tetrads. As a consequence, more than eight mini-microspores of different sizes were produced by one tetrad. Genomic in situ hybridization results indicated that no chromosome replication occurred during such divisions. In some tetrads, the four nuclei were fused to form one large cell with increased chromosome number. The extra divisions or fusions appeared only in some flower buds of one plant, some anthers in the same buds, or even in individual cells of tetrads. The possible mechanisms behind these cytological phenomena are discussed.     

Outer membrane peptides ofYersinia pestis mediating siderophore-independent assimilation of iron

Summary It is established that wild-type cells ofYersinia pestis absorb exogenous hemin or Congo red and thus grow as pigmented colonies at 26° C on media containing these chromatophores (Pgm⁺). Pgm⁺ isolates are known to possess a siderophore-independent mechanism of iron-transport (required for growth in iron-deficient medium) which is absent in avirulent Pgm^– mutants. Production of the bacteriocin pesticin and linked invasins (Pst⁺) is an additional defined virulence factor of yersiniae; mutation of Pgm⁺,Pst^– organisms to pesticin-resistance (Pst^r) results in concomitant conversion to Pgm^–. In this study, autoradiograms of two-dimensional gels of [³⁵S]methionine-labeled outer membranes from Pgm^– mutants were compared to those of the Pgm⁺,Pst⁺ or Pgm⁺,Pst^– parent. An apparently single predominant peptide present in these preparations (> 10% of total membrane protein) existed as a family of iron-modifiable 17.9-kDa molecules focusing down to isoelectric points of about 4.6 and up to 5.89. Expression of eight detectable Pst⁺-specific peptides was not significantly influenced by exogenous iron. Pgm⁺ yersiniae constitutively produced pigmentation-specific peptide F and five iron-repressible peptides termed IrpA to IrpE. Typical spontaneous mutation to Pgm^– resulted in loss of peptide F and IrpB-E. A rare Pgm⁺,Pst^r mutant, selected on Congo red agar containing pesticin, also lost IrpB-E but retained peptide F. This isolate, like Pgm^– mutants, failed to grow in iron-deficient medium. Regardless of phenotype, all yersiniae utilized hemin, hemopexin, myoglobin, hemoglobin, and ferritin, but not transferrin or lactoferrin, as sole sources of iron.This is journal article no. 13025 of the Michigan Agricultural Experiment Station.     

Molecular Epidemiology of Clostridium difficile at a Medical Center in Taiwan: Persistence of Genetically Clustering of A?B+ Isolates and Increase of A+B+ Isolates

Introduction

We investigated the changing trend of various toxigenic Clostridium difficile isolates at a 3 500-bed hospital in Taiwan. Genetic relatedness and antimicrobial susceptibility of toxigenic C. difficile isolates were also examined.

Methods

A total of 110 non-repeat toxigenic C. difficile isolates from different patients were collected between 2002 and 2007. Characterization of the 110 toxigenic isolates was performed using agar dilution method, multilocus variable-number tandem-repeat analysis (MLVA) genotyping, tcdC genotyping, and toxinotyping.

Results

Among the 110 toxigenic isolates studied, 70 isolates harbored tcdA and tcdB (A⁺B⁺) and 40 isolates harbored tcdB only (A⁻B⁺). The annual number of A⁺B⁺ isolates considerably increased over the 6-year study (P = 0.055). A total of 109 different MLVA genotypes were identified, in which A⁺B⁺ isolates and A⁻B⁺ isolates were differentiated into two genetic clusters with similarity of 17.6%. Twenty-four (60%) of the 40 A⁻B⁺ isolates formed a major cluster, MLVA-group 1, with a similarity of 85%. Seven (6.4%) resistant isolates were identified, including two metronidazole-resistant and five vancomycin-resistant isolates.

Conclusions

This study indicated a persistence of a MLVA group 1 A⁻B⁺ isolates and an increase of A⁺B⁺ isolates with diverse MLVA types. Moreover, C. difficile isolates with antimicrobial resistance to metronidazole or vancomycin were found to have emerged. Continuous surveillance is warranted to understand the recent situation and control the further spread of the toxigenic C. difficile isolates, especially among hospitalized patients.     

A general method for isolation of Mu d1-8(Aprlac) operon fusions in Salmonella typhimurium LT2 from Tn10 insertion strains: chlC::Mu d1-8

Summary A general method was developed for the isolation of Salmonella thyphimurium LT2 Mu d1–8 (Ap^r lac) operon fusions in a gene displacing a Tn10 insertion. Random Mu d1–8 fusion pools were prepared to grow phage P22 lysates which transduced chlC::Tn10 to Ap^rTet^s on fusaric acidampicillin plates. Among these Ap^rTet^s potential chlC::Mu d1–8 fusions, a simple spot test identified the fusions that were closely linked to the Tn10 insertion in chlC. Out of 68 Ap^rTet^s isolates 7 chlC::Mu d1–8 fusions with a nitrate-induced Lac⁺ phenotype were obtained. When oxrA::Tn10 was transduced into these chlC::Mu d1–8 fusions, they became Lac^- even in the presence of nitrate, confirming that they were chlC::Mu d1–8 fusions.     

Conversion of<Emphasis Type="Italic">G. hansenii</Emphasis> PJK into non-cellulose-producing mutants according to the culture condition

The conversion of a cellulose-producing cell (Cel ⁺) fromGluconacetobacter hansenii PJK (KCTC 10505 BP) to a non-cellulose-producing cell (Cel ⁻) was investigated by measuring the colony forming unit (CFU). This was achieved in a shaking flask with three slanted baffles, which exerted a strong shear stress. The addition of organic acid, such as glutamic acid and acetic acid, induced the conversion of microbial cells from a wild type toCel ⁻ mutants in a flask culture. The supplementation of 1% ethanol to the medium containing an organic acid depressed the conversion of the microbial cells toCel ⁻ mutants in a conventional flask without slanted baffles. The addition of ethanol to the medium containing an organic acid; however, accelerated the conversion of microbial cells in the flask with slanted baffles. TheCel ⁺ cells from the agitated culture were not easily converted intoCel ⁻, mutants on the additions of organic acid and ethanol to a flask without slanted baffles, but some portion of theCel ⁺ cells were converted toCel ⁻ mutants in a flask with slanted baffles. The conversion ratio ofCel ⁺ cells toCel ⁻ mutants was strongly related to the production of bacterial cellulose independently from the cell growth.     

Disruption of <Emphasis Type="Italic">RCI2A</Emphasis> leads to over-accumulation of Na<Superscript>+</Superscript> and increased salt sensitivity in <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis> plants

For plant salt tolerance, it is important to regulate the uptake and accumulation of Na⁺ ions. The yeast pmp3 mutant which lacks PMP3 gene accumulates excess Na⁺ ions in the cell and shows increased Na⁺ sensitivity. Although the function of PMP3 is not fully understood, it is proposed that PMP3 contributes to the restriction of Na⁺ uptake and consequently salt tolerance in yeasts. In this paper, we have investigated whether the lack of RCI2A gene, homologous to PMP3 gene, causes a salt sensitive phenotype in Arabidopsis (Arabidopsis thaliana (L.) Heynh.) plants; and to thereby indicate the physiological role of RCI2A in higher plants. Two T-DNA insertional mutants of RCI2A were identified. Although the growth of rci2a mutants was comparable with that of wild type under normal conditions, high NaCl treatment caused increased accumulation of Na⁺ and more reduction of the growth of roots and shoots of rci2a mutants than that of wild type. Undifferentiated callus cultures regenerated from rci2a mutants also accumulated more Na⁺ than that from wild type under high NaCl treatment. Furthermore, when wild-type and rci2a plants were treated with NaCl, NaNO₃, Na₂SO₄, KCl, KNO₃, K₂SO₄ or LiCl, the rci2a mutants showed more reduction of shoot growth than wild type. Under treatments of tetramethylammonium chloride, CaCl₂, MgCl₂, mannitol or sorbitol, the growth reduction was comparable between wild-type and rci2a plants. These results suggested that RCI2A plays a role directly or indirectly for avoiding over-accumulation of excess Na⁺ and K⁺ ions in plants, and contributes to salt tolerance.     

Bacillus thuringiensis crystal protein (δ-endotoxin) gene expression is independent of early sporulation specific functions

Bacillus thuringiensis produces a parasporal insecticidal crystal protein. The correlation between sporulation and crystal protein production inBacillus thuringiensis var.israelensis was studied. The strain was made resistant’against streptomycin (St^R)-Acrystalliferous (Cry^-) cured derivatives and asporogenous acrystalliferous (Spo⁻ Cry⁻) mutants blocked at an early stage of sporulation were isolated. Plasmid transfer experiments were performed between St^R Spo⁺ Cry⁺ (streptomycin sensitive sporogeneous crystalliferous) and St^RR Spo⁺ Cry⁻ and also between St^s Spo⁺ Cry⁺ and St^R Spo⁻ Cry⁻ strains. StR colonies were selected. Insect toxicity was exhibited by the St^R isolates in both the cases. The process of crystal formation is, therefore, independent of early sporulative events.     

Nitrate and nitrite reductase negative mutants of N2-fixingAzospirillum spp.

Chlorate resistant spontaneous mutants ofAzospirillum spp. (syn.Spirillum lipoferum) were selected in oxygen limited, deep agar tubes with chlorate. Among 20 mutants fromA. brasilense and 13 fromA. lipoferum all retained their functional nitrogenase and 11 from each species were nitrate reductase negative (nr^–). Most of the mutants were also nitrite reductase negative (nir^–), only 3 remaining nir⁺. Two mutants from nr⁺ nir⁺ parent strains lost only nir and became like the nr⁺ nir^– parent strain ofA. brasilense. No parent strain or nr⁺ mutant showed any nitrogenase activity with 10 mM NO ₃ ^– . In all nr^– mutants, nitrogenase was unaffected by 10 mM NO ₃ ^– . Nitrite inhibited nitrogenase activity of all parent strains and mutants including those which were nir^–. It seems therefore, that inhibition of nitrogenase by nitrate is dependent on nitrate reduction. Under aerobic conditions, where nitrogenase activity is inhibited by oxygen, nitrate could be used as sole nitrogen source for growth of the parent strains and one mutant (nr^– nir^–) and nitritite of the parent strains and 10 mutants (all types). This indicates the loss of both assimilatory and dissimilatory nitrate reduction but only dissimilatory nitrite reduction in the mutants selected with chlorate.     

The effect of spo0 mutations on the expression of spo0A- and spo0F-lacZ fusions

Summary We have constructedspo0A-lacZ andspo0F-lacZ fusions with a temperate phage vector and have investigated howspo0 gene products are involved in the expression of each of these genes. The expression ofspo0A-lacZ andspo0F-lacZ was stimulated at about the time of cessation of vegetative growth in Spo⁺ cells. This stimulation ofspo0A-lacZ was impaired by mutations in thespo0B, D, E, F orH genes but was not affected by mutations in thespo0J orK genes. Similar results were obtained with thespo0F-lacZ fusion. The effect of thespo0A mutation onspo0A-lacZ expression was characteristic: thespo0A-directed β-galactosidase activity found during vegetative growth was significantly enhanced in thespo0A mutant. This result suggests thatspo0A gene expression is autoregulated being repressed by its own gene product. Another remarkable observation was the effect of thesof-1 mutation, which is known to be aspo0A allele; it suppressed the sporulation deficiency ofspo0B, spo0D andspo0F mutants. Thespo0A-lacZ stimulation, which is impaired by any one of thesespo0 mutations, was restored by the additionalsof-1 mutation.     

Competitive abilities of Tn5 Tox- mutants of a rhizobacterium inhibitory to wheat growth

Antibiosis has been thought to impart a competitive advantage to soil microorganisms. A rhizobacterium of the genus Pseudomonas produces a toxin that inhibits the growth of other microorganisms and winter wheat (Triticum aestivum L.). The bacterium was mutagenized with the Tn5 transposon to obtain toxin-negative (Tox^-) mutants or was selected for its spontaneous resistance to rifampicin. Tox^- mutants were used to determine the role of the toxin in wheat root inhibition, root colonization, and rhizosphere competitiveness. Four Tox^- (loss of inhibition of both E. coli and wheat root growth) and four partial Tox⁺ (partial loss of inhibition of E. coli and wheat root growth) Tn5 mutants were isolated. Seven of the mutants had different Tn5 chromosomal insertions, which suggests that toxin production is the result of several gene loci. Competitive root-colonization abilities of the Tox^- isolates were studied in winter wheat rhizospheres using varied population levels in autoclaved and nonautoclaved soil. Toxin production did not affect the competitive abilities of these organisms with native soil microflora. Results here indicate that toxin production by these organisms is not the primary mechanism of their competitive advantage in root colonization. Thus, opportunities exist for biological control of plant-suppressive bacteria using these Tox^- strains.     

Functional Analysis of the Na+/H+ Antiporter Encoding Genes of the Cyanobacterium Synechocystis PCC 6803

The role of putative Na⁺/H⁺ antiporters encoded by nhaS1 (slr1727), nhaS3 (sll0689), nhaS4 (slr1595), and nhaS5 (slr0415) in salt stress response and internal pH regulation of the cyanobacterium Synechocystis PCC 6803 was investigated. For this purpose the mutants (single, double, and triple) impaired in genes coding for Na⁺/H⁺ antiporters were constructed using the method of interposon mutagenesis. PCR analyses of DNA demonstrated that mutations in nhaS1, nhaS4, and nhaS5 genes were segregated completely and the mutants contained only inactivated copies of the corresponding genes. Na⁺/H⁺ antiporter encoded by nhaS3 was essential for viability of Synechocystis since no completely segregated mutants were obtained. The steady-state intracellular sodium concentration and Na⁺/H⁺ antiporter activities were found to be the same in the wild type and all mutants. No differences were found in the growth rates of wild type and mutants during their cultivation in liquid media supplemented with 0.68 M or 0.85 M NaCl as well as in media buffered at pH 7.0, 8.0, or 9.0. The expression of genes coding for Na⁺/H⁺ antiporters was studied. No induction of any Na⁺/H⁺ antiporter encoding gene expression was found in wild type or single mutant cells grown under high salt or at different pH values. Nevertheless, in cells of double and triple mutants adapted to high salt or alkaline pH some of the remaining Na⁺/H⁺ antiporter encoding genes showed induction. These results might indicate that some of Na⁺/H⁺ antiporters can functionally replace each other under stress conditions in Synechocystis cells lacking the activity of more than one antiporter.     

Characterization of poly(A+)RNA in free messenger ribonucleoprotein and polysomes of mouse Taper ascites cells

Cytoplasmic extracts of mouse Taper ascites cells were centrifuged on sucrose gradients to give 0–80 S, monosome, and polysome fractions. CsCl equilibrium density centrifugation of formaldehyde-fixed material from the 0–80 S fraction demonstrated that the messenger RNA in the 0–80 S fraction was in the form of free ribonucleoprotein. The size of the poly(A⁺)RNA and the size of the poly(A) segments of these molecules were shown to be very similar in both the free mRNP² and polysome fractions. The labeling kinetics of the free mRNP poly(A⁺)RNA was similar to that of the polysomal poly(A⁺)RNA.The free mRNP poly(A⁺)RNA efficiently stimulated protein synthesis in the wheat germ cell-free system, supporting the view that it was mRNA. Two-dimensional gel electrophoresis was used to analyze the proteins whose synthesis was directed by free mRNP and polysomal poly(A⁺)RNA. The free mRNP poly(A⁺)RNA directed the synthesis of a simpler set of abundant protein products than did the polysomal poly(A⁺)RNA. Most of the free mRNP abundant protein products were also present in the polysomal products, though obvious quantitative differences were evident, indicating that each individual mRNA had its own characteristic distribution between polysomes and the translationally inactive RNP form.     

A topological model for the haemolysin translocator protein HlyD

Summary A topological model for HlyD is proposed that is based on results obtained with gene fusions of lacZ and phoA to hlyD. Active H1yD-LacZ fusion proteins were only generated when lacZ was fused to hlyD. within the first 180 by (60 amino acids). H1yD-PhoA proteins exhibiting alkaline phosphatase (AP) activity were obtained when phoA was inserted into hlyD. between nucleotides 262 (behind amino acid position 87) and 1405 (behind amino acid position 468, only 10 amino acids away from the C-terminus of HlyD Active insertions of phoA into the middle region of hlyD. were not observed on in vivo transposition but such fusions exhibiting AP activity could be constructed by in vitro techniques. A fusion protein that carried the PhoA part close to the C-terminal end of HlyD proved to be the most stable HlyD-PhoA fusion protein. In contrast to the other, rather unstable, HlyD-PhoA⁺ fusions, no proteolytic degradation product of this HlyD-PhoA protein was observed and nearly all the alkaline phosphatase activity was membrane bound. Protease accessibility and cell fractionation experiments indicated that the alkaline phosphatase moiety of this fusion protein was located in the periplasm as for all other HlyD-PhoA⁺ proteins. These data and computer-assisted predictions suggest a topological model for HlyD with the N-terminal 60 amino acids located in the cytoplasm, a single transmembrane segment from amino acids 60 to 80 and a large periplasmic region extending from amino acid 80 to the C-terminus. Neither the HlyD fusion proteins obtained nor a mutant HlyD protein that had lost the last 10 amino acids from the C-terminus of HlyD exhibited translocator activity for HlyA or other reporter proteins carrying the HlyA signal sequence. The C-terminal 10 amino acids of HlyD showed significant similarity with the corresponding sequences of other HlyD-related proteins involved in protein secretion.