Morphologically normal-appearing mammary epithelial cells obtained from high-risk women exhibit methylation silencing of INK4a/ARF

PURPOSE

p16(INK4a) has been appreciated as a key regulator of cell cycle progression and senescence. Cultured human mammary epithelial cells that lack p16(INK4a) activity have been shown to exhibit premalignant phenotypes, such as telomeric dysfunction, centrosomal dysfunction, a sustained stress response, and, most recently, a dysregulation of chromatin remodeling and DNA methylation. These data suggest that cells that lack p16(INK4a) activity would be at high risk for breast cancer development and may exhibit an increased frequency of DNA methylation events in early cancer.

EXPERIMENTAL DESIGN

To test this hypothesis, the frequencies of INK4a/ARF promoter hypermethylation, as well as four additional selected loci, were tested in the initial random periareolar fine needle aspiration samples from 86 asymptomatic women at high risk for development of breast cancer, stratified using the Masood cytology index.

RESULTS

INK4a/ARF promoter hypermethylation was observed throughout all early stages of intraepithelial neoplasia and, importantly, in morphologically normal-appearing mammary epithelial cells; 29 of 86 subjects showed INK4a/ARF promoter hypermethylation in at least one breast. Importantly, INK4a/ARF promoter hypermethylation was not associated with atypia, and the frequency of hypermethylation did not increase with increasing Masood cytology score. The frequency of INK4a/ARF promoter hypermethylation was associated with the combined frequency of promoter hypermethylation of retinoic acid receptor-beta2, estrogen receptor-alpha, and breast cancer-associated 1 genes (P = 0.001).

CONCLUSIONS

Because INK4a/ARF promoter hypermethylation does not increase with age but increases with the frequency of other methylation events, we predict that INK4a/ARF promoter hypermethylation may serve as a marker of global methylation dysregulation.

Portable digital assistants (PDAs) in dentistry: part II--pilot study of PDA use in the dental clinic

AIM

To describe a simple technical evaluation of the access, security issues and uses of wireless networked PDAs in a dental clinic and report a pilot study investigating students' educational use of PDAs to access a Virtual Learning Environment (VLE) in a dental clinic.

OBJECTIVES

To undertake a technical evaluation of wireless networking to PDAs focusing on security issues, robustness of the system and accessibility particularly to educational resources. To evaluate the impact of using a PDA on undergraduate students in the dental clinic and at home.

DESIGN

Part II describes the technical and educational evaluation of PDAs used by one group of 12 undergraduate fourth year students in the Primary Dental Care clinic. A cross over trial of six students with PDAs and six without was carried out during one semester of 12 weeks.

METHODS

Technical issues such as secure internet access using wireless connectivity were addressed. An assessment of the general and educational use and the students' attitudes towards using PDAs was undertaken using online questionnaires and focus group discussions.

RESULTS

Over 90% of participants wanted PDAs as part of their dental kit. The potential of PDA use in dental training was demonstrated by a good to excellent response by over 75% of participants to having access to online support materials, particularly videos, being able to make notes for individual study and to keep a diary of their commitments to teaching sessions. Recreational use included a 100% good to excellent response to playing games and keeping a diary.

CONCLUSION

The PDA proved to be a convenient and versatile mode of access to online education. Technical solutions enabled a substantial proportion of the functionality of WebCT (Web Course Tools) to be accessed by the students in a clinical environment. Both novice and experienced users were able to appreciate the use of the PDA and the less able considered that their ICT skills had improved. However, further research is needed to determine how students use a range of new technologies in their undergraduate programmes. The Dental Institute plans to recommend that all students will use this device in the future throughout their five-year curriculum, and the scoping of the implications of this recommendation is underway.

Portable Digital Assistants (PDAs) in dentistry: Part I

AIM

To provide a basic understanding of the features of a portable digital assistant (PDA) and how it may be useful for the general dental practitioner.

OBJECTIVES

To outline the various types, functions and applications of a PDA and suggest its use for the dental professional now and in the future. To enable appreciation of the technology and educational evaluation carried out in the pilot study reported in Part II.

DESIGN

Part I is a descriptive account of the use and function of the PDA in dentistry and its potential for the future.

METHOD

A review of the literature was carried out drawing on evidence from general healthcare and assessments of portable computing aids evaluated in a dentally related setting. RESULTS Choosing a PDA for use in dental practice is complex but should be based on the user's needs mapped to key features, size and cost of the device.

CONCLUSION

No ideal customisable mobile digital solution currently exists but evidence from general healthcare use suggests that there are valuable features that can aid the general dental practitioners such as personal management and point of source assistance.

Tumor Suppressor p16INK4A Regulates Polycomb-mediated DNA Hypermethylation in Human Mammary Epithelial Cells

Alterations in DNA methylation are important in cancer, but the acquisition of these alterations is poorly understood. Using an unbiased global screen for CpG island methylation events, we have identified a non-random pattern of DNA hypermethylation acquired in p16-repressed cells. Interestingly, this pattern included loci located upstream of a number of homeobox genes. Upon removal of p16(INK4A) activity in primary human mammary epithelial cells, polycomb repressors, EZH2 and SUZ12, are up-regulated and recruited to HOXA9, a locus expressed during normal breast development and epigenetically silenced in breast cancer. We demonstrate that at this targeted locus, the up-regulation of polycomb repressors is accompanied by the recruitment of DNA methyltransferases and the hypermethylation of DNA, an endpoint, which we show to be dependent on SUZ12 expression. These results demonstrate a causal role of p16(INK4A) disruption in modulating DNA hypermethylation, and identify a dynamic and active process whereby epigenetic modulation of gene expression is activated as an early event in breast tumor progression.

Investigation into potential mechanisms promoting biocompatibility of polymeric biomaterials containing the phosphorylcholine moiety

Phosphorylcholine (PC) moieties were chemically attached to surfaces of polymer microparticles by addition of 2-methylacryloyloxyethyl phosphorylcholine monomer to the seeded, semi-continuous polymerisations of methyl methacrylate (MMA) and butyl acrylate (BA). The surface of the bio-functionalised polymer microparticles was principally characterised using X-ray photoelectron spectroscopy (XPS), dynamic nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM), photon correlation spectroscopy (PCS), acoustophoresis and enzyme-linked immunosorbent assays (ELISA). It was found that the persulphate initiating species are concealed behind the phosphorylcholine containing monomer sequence located on the surface of the microparticles. The combination of analytical techniques showed that the surfaces of the polymer microparticles are extremely mobile above the glass transition temperature of the co-polymer and able to rearrange depending on the environment in which they are placed. This allows the phosphorylcholine moiety to be preferentially expressed at the surface in aqueous media, but not so in the dry state or conditions of ultra-high vacuum. In terms of the nature of the biocompatibility of phosphorylcholine containing polymers, no evidence was found for the irreversible structuring of water molecules around the phosphorylcholine moiety in the wet state. The results of this work suggest that a more likely contributory reason for the protein-resistant nature of phosphorylcholine containing polymers is the mobility of the phosphorylcholine moiety. Increases in biocompatibility correspond with increases in the hydrophilicity of a polymer surface when phosphorylcholine is preferentially expressed. A large free water fraction may be present in the phosphorylcholine containing monomer sequence, as part of a hydrogel structure located at the surface of the polymer microparticles. This, coupled with concomitant modification of the local electrical double-layer very close to the surface may also play a critical role in reducing protein-surface interactions.

The Anglo-Italian collaboration: a report of the first steps in implementing the Bologna Declaration

This report summarises the accomplishments of King's College London and Università degli Studi di Brescia in establishing an Anglo-Italian Collaboration. The aim was to develop areas of enterprise in clinical practice, teaching and research that reflected the principles of the Bologna Declaration.

Identification of a DNA-binding site and transcriptional target for the EWS-WT1(+KTS) oncoprotein

Desmoplastic small round cell tumor (DSRCT) is defined by a chimeric transcription factor, resulting from fusion of the N-terminal domain of the Ewing's sarcoma gene EWS to the three C-terminal zinc fingers of the Wilms' tumor suppressor WT1. Although DNA-binding sites have been defined for the uninterrupted WT1 zinc finger domains, the most prevalent isoforms of both WT1 and EWS-WT1 have an insertion of three amino acids [lysine, threonine, and serine (KTS)], which abrogates binding to known consensus sequences and transactivation of known target genes. Here, we used cDNA subtractive hybridization to identify an endogenous gene, LRRC15, which is specifically up-regulated after inducible expression of EWS-WT1(+KTS) in cancer cell lines, and is expressed within primary DSRCT cells. The chimeric protein binds in vitro and in vivo to a specific element upstream of LRRC15, leading to dramatic transcriptional activation. Mutagenesis studies define the optimal binding site of the (+KTS) isoform of EWS-WT1 as 5'-GGAGG(A/G)-3'. LRRC15 encodes a leucine-rich transmembrane protein, present at the leading edge of migrating cells, the expression of which in normal tissues is restricted to the invasive cytotrophoblast layer of the placenta; small interfering (siRNA)-mediated suppression of LRRC15 expression in breast cancer cells leads to abrogation of invasiveness in vitro. Together, these observations define the consequence of (KTS) insertion within WT1-derived zinc fingers, and identify a novel EWS-WT1 transcriptional target implicated in tumor invasiveness.

Induction of BAIAP3 by the EWS-WT1 chimeric fusion implicates regulated exocytosis in tumorigenesis

Desmoplastic small round cell tumor (DSRCT) is defined genetically by the chimeric fusion of the Ewing's sarcoma and Wilms' tumor genes, generating a novel transcription factor, EWS-WT1. By using cells with inducible EWS-WT1 to screen high-density microarrays, we identified BAIAP3 as a transcriptional target of the chimera. The BAIAP3 promoter is specifically bound in vivo by the (-KTS) isoform of EWS-WT1, consistent with its activation in reporter assays. BAIAP3 encodes a protein implicated in regulated exocytosis, which is colocalized with a secreted growth factor within cytoplasmic organelles. Ectopic expression of BAIAP3 in tumor cells dramatically enhances growth in low serum and colony formation in soft agar. BAIAP3 therefore encodes a transcriptional target of an oncogenic fusion protein that implicates the regulated exocytotic pathway in cancer cell proliferation.

Induction of the interleukin-2/15 receptor beta-chain by the EWS-WT1 translocation product

EWS-WT1 is a chimeric transcription factor resulting from fusion of the N-terminal domain of the Ewing sarcoma gene EWS to the three C-terminal zinc fingers of the Wilms tumor suppressor WT1. This translocation underlies desmoplastic small round cell tumor (DSRCT), which is noted for the abundance of reactive stroma surrounding islets of tumor cells, suggestive of paracrine signals contributing to tumor cell proliferation. Hybridization to high-density oligonucleotide microarrays can be used to identify targets of EWS-WT1. Expression of EWS-WT1 from a tetracycline-regulated promoter leads to the induction of growth-associated genes, of which the most remarkable is the beta-chain of the interleukin-2/15 receptor (IL-2/15Rbeta). Potent transcriptional activation by the chimeric protein maps to two bindings sites within the IL-2/15Rbeta promoter. Analysis of primary DSRCT tumor specimens demonstrates high levels of IL-2/15Rbeta within the tumor cells, along with expression of IL-2 and IL-15 by the abundant hyperplastic endothelial cells within the reactive stroma. Activation of this cytokine signaling pathway is consistent with the nuclear localization of its downstream effectors, phosphorylated STAT3 and STAT5. These observations suggest that the transcriptional induction of a cytokine receptor by a tumor-associated translocation product enables a proliferative response of epithelial cancer cells to ligands secreted by the surrounding stroma.

Tetrachlorobis(N1-phenylacetamidino-kappaN2)rhenium(IV) at 11 K by X-ray diffraction and at 20 K by neutron diffraction

The crystal structure of the title compound, [ReCl(4)(C(8)H(10)N(2))(2)], has been determined by X-ray diffraction at 11 K and by neutron diffraction at 20 K. The accurate and extensive data sets lead to more precise determinations than are available from earlier work. The agreement in atomic positional and displacement parameters at these very low temperatures is good. The results will facilitate re-examination of the magnetic structure of the complex. The Re atom lies on a special position and the molecule has twofold crystallographic symmetry.

Participating dentists' assessment of the pilot regional online videoconferencing in dentistry (PROVIDENT) project

OBJECTIVE

To assess the educational effectiveness of delivering continuing professional education (CPE) from dental schools to small groups of dentists at distant sites via videoconferenced links using relatively inexpensive equipment and ISDN2 links.

DESIGN

41 videoconferences between the four campuses of London Dental Schools and postgraduate centres in South East England were assessed using a pre-piloted questionnaire which contained open and specific questions. The questionnaire was given to all participants at the end of each videoconference. Answers to the specific questions were graded using the Likert scale.

RESULTS

40 of the 41 videoconferences were completed satisfactorily and were attended by 257 participants, all of whom completed questionnaires. However, no individual question was answered by all the participants. Of the responses 90% were positive on the topics of appropriateness of the teaching material for delivery by videoconference and of its educational level. 90% of responses also indicated a wish to attend further videoconferences and satisfaction at avoiding the need to travel to London for similar educational activity. 87% rated the lecturers as good or excellent in their use of the medium. 85% of responses indicated that the question and answer sessions within the videoconferences were useful and 82% that the visual aids enhanced the sessions. The technical aspects of the videoconferences were rated positively but to a lesser extent than the educational aspects with 69% of positive responses for visibility of visual aids, 54% for sound quality and 76% for the lecturers use of the technology. The technical aspects of the videoconferences improved during the pilot study. In response to the open questions, participants stated that they found the most useful aspects of the videoconferences were not having to travel, access to first rate lecturers, the discussions and the opportunity to interact with experts.

CONCLUSIONS

The participants in this pilot study were positive about the use of videoconferencing to deliver educational material from dental schools to small groups. Once the technology has improved, this medium has the potential to provide CPE for dentists at work or at home in response to their specific needs.

A study of videoconferencing for postgraduate continuing education in dentistry in the UK--the teachers' view

Videoconferencing is an established method for providing medical education over long distances. Our aims were to assess the feasibility of videoconferencing in dental postgraduate education, to evaluate its practicability, teacher satisfaction and evaluate equipment. Twenty-seven teachers from the 4 London Dental Schools provided 41 postgraduate dental education sessions on a range of topics to regional postgraduate centres and dental practices as part of the Thames Health Region's programme. Videoconferencing was carried out using a relatively inexpensive personal computer system link using ISDN2 telephone lines and Z350 protocol. Presenter views and assessment were obtained by questionnaire, interview and videotape. Teachers felt that minimal additional preparation time was required for videoconferencing and 21/27 preferred it to in-person teaching, most noting the saving in travel time. Only 3 of the teachers were dissatisfied with their ability to communicate, 4 were equivocal and 20 were either pleased or very pleased. The teachers largely enjoyed the experience and performed well in the new medium. However, sound quality proved inadequate in 5/41 links and most sessions included some periods of suboptimal sound. Only 4 teachers were satisfied with their ability to perform question and answer interaction with the audience. We conclude that experienced teachers adapt readily to videoconferencing and learn to communicate effectively very quickly. Teachers were positive about the medium despite its shortcomings and improvements in sound quality would allow a rapid expansion of postgraduate dental education by videoconference.

Loss of heterozygosity at 7p in Wilms' tumour development

Chromosome 7p alterations have been implicated in the development of Wilms' tumour (WT) by previous studies of tumour cytogenetics, and by our analysis of a constitutional translocation (t(1;7)(q42;p15)) in a child with WT and radial aplasia. We therefore used polymorphic microsatellite markers on 7p for a loss of heterozygosity (LOH) study, and found LOH in seven out of 77 informative WTs (9%). The common region of LOH was 7p15-7p22, which contains the region disrupted by the t(1;7) breakpoint. Four WTs with 7p LOH had other genetic changes; a germline WT1 mutation with 11p LOH, LOH at 11p, LOH at 16q, and loss of imprinting of IGF2. Analysis of three tumour-associated lesions from 7p LOH cases revealed a cystic nephroma-like area also having 7p LOH. However, a nephrogenic rest and a contralateral WT from the two other cases showed no 7p LOH. No particular clinical phenotype was associated with the WTs which showed 7p LOH. The frequency and pattern of 7p LOH demonstrated in our studies indicate the presence of a tumour suppressor gene at 7p involved in the development of Wilms' tumour.

Localization of a novel t(1;7) translocation associated with Wilms' tumor predisposition and skeletal abnormalities

Cytogenetic analysis of predisposition syndromes has played a critical role in the elucidation of the genetics of Wilms' tumor (WT). Therefore, we became interested in a patient who presented with a WT and a nephrogenic rest in the contralateral kidney (suggestive of a predisposition) and a de novo t(1;7)(q42;p15) constitutional translocation as the only visible cytogenetic abnormality. He also had bilateral radial aplasia and other skeletal abnormalities, but there was no manifestation of any syndrome previously associated with WT. In the tumor, the translocation was retained, and the other 7p region was lost by the formation of an isochromosome i(7q). Here, we report the localization of the chromosome 7 breakpoint within a yeast artificial chromosome (YAC) contig by using fluorescence in situ hybridization (FISH), localizing the breakpoint between markers sWSS355 and sWSS1449. A number of YACs span the breakpoint and, thus, contain the region that is disrupted by the translocation. This may represent the site of a novel tumor suppressor gene that is involved in WT and also in normal renal development.

Structures of Some Complexes Containing the ReIVCl4 Unit

The X-ray crystal structure determinations of five complexes of rhenium(IV) containing the ReCl4L2 unit, with L monodentate , are reported, one at 92 K. They are: (1) cis -( HNCMeNHPh )2ReCl4, Pccn , a 21.677(4), b 7.253(1), c 12.470(2) Ǻ, R1(2σ) 0.0217, Rw 0.0473; (2) the di ( acetonitrile ) solvate of (1), Pī , a 10.005(2), b 12.120(2), c 12.744(2) Ǻ, α 72.19(1), β 67.65(1), γ 90.95(1)°, R1(2σ) 0.0311, Rw 0.0819; (3) cis -(HN= CMeNH (p-C6H4Me))2ReCl4, Pna21, a 12.782(2), b 8.237(1), c 21.279(3) Ǻ, R1(2σ) 0.0497, Rw 0.1066; (4) cis-( thf )2ReCl4, P 212121, a 7.785(2), b 12.666(4), c 14.253(5) Ǻ, R1(2σ), 0.0326, Rw 0.0827; and (5) trans-(Me2PhP)2ReCl4, P 21/c, a 9.701(2), b 13.739(6), c 8.324(2) Ǻ, β 106.83(2), R1(2σ) 0.0241, Rw 0.0613. The Re-Cl bond lengths in these and six other ReIVCl4L2 octahedral complexes are compared, and no distinct trans-effect of the donor atom on the chlorine atoms is seen either where L is monodentate as in our compounds or where L2 is a chelate ligand, as in the examples from the literature, although the results are much less clear there.

Low-Temperature Structure and Magnetic Properties of Tetraphenylarsonium Tetrachloronitridotechnetate(VI)

The crystal structure of [As(C6H5)4] [TcNCl4] was determined at 120 K by X-ray diffraction and at 28 K by neutron diffraction. The crystals are tetragonal, space group P4/n, with a 1260.4(3) and c 773.2(2) pm at 120 K. The [TcNCl4]-anion possesses exact C4v symmetry, with Tc≡N distances of 160.3(2) and 162.5(4)pm at 120 and 28 K respectively. Magnetic susceptibilities were measured on single crystals from 300 to 4.5 K. The results indicate a well behaved S ½ system following the Curie-Weiss law with θ -0.13 K

Protein quality of enteral nutrition products is consistent with label claims during shelf life and beyond expiration date

OBJECTIVE

Eternal formulas were monitored during their shelf life and beyond expiration date to examine protein quality.

DESIGN

Protein quality was determined by protein efficiency ratio (PER) bioassays and amino acid analyses.

SETTING

A certified laboratory performed the PER tests according to procedures established by the Association of Official Analytical Chemists and recognized by the US Food and Drug Administration (FDA). The amino acid analyses were performed in our laboratory using validated methods.

SAMPLES

Commercially available formulas (Ensure, Osmolite HN, TwoCal HN) that contained protein blends of caseinates or caseinates with soybean protein isolate were studied.

MAIN OUTCOME MEASURES

Achievement of protein-quality values greater than or equal to 70% of the fresh reference casein value as determined by the PER method would be consistent with adequate protein quality as described by the FDA. Levels of indispensable amino acids that meet or exceed the standards established by the National Research Council of the National Academy of Sciences are considered high-quality proteins. Levels of amino acids throughout shelf life were compared with published label claims.

RESULTS

Amino acid analyses, which included measurement of tryptophan and total sulfur amino acids, revealed that both fresh and outdated products met or exceeded standards for proteins of high biologic value and were consistent with label claims. The PER values ranged from 90% to 96% of the control diet for fresh product and 82% to 87% for products evaluated after expiration.

CONCLUSION

The enteral products studied provide high-quality protein throughout the shelf life of the product.

The Conformations of the Hexaammineruthenium(III) Ion in Simple Salts

Single-crystal X-ray diffraction results are presented for six hexaammineruthenium (III) salts, viz. [ Ru (NH3)6]2(SO4)35H2O, [ Ru (NH3)6] CdCl5, [ Ru (NH3)6]ZnCl5, [ Ru (NH3)6]Cl2SCN, [ Ru (NH3)6]2(S2O6)3.H2O, and a salt of approximate formula [ Ru (NH3)6]2 [POF5]3.4H2O. The 11 independent cations in these and other published structures do not adopt a single conformation in respect of hydrogen atom disposition. Analysis of the N- Ru -N-H dihedral angles and their correlations strongly suggests that the conformation is random, given the crystallographic site symmetry. The structure with torsional energy calculated at a minimum by ab initio methods is not observed. This suggests that there are only a limited number of interionic geometries feasible in crystallization. Such a limitation suggests that computing crystal structures, with no assumptions as to space group or any other assumption, is not an open-ended problem with excessive alternatives.

Single-Crystal Magnetic Properties of [Co(NH3)5(OH2)] [Cr(CN)6] Between 2 and 300 K

The magnetic susceptibilities along and perpendicular to the c axis (hexagonal setting) between 2.0 and 300 K at a magnetic field of 1.00 T, and the magnetizations at field strengths up to 5.00 T, are presented for single crystals of [Co(NH3)5(OH2)] [Cr(CN)6]. The results are interpreted in terms of zero-field splitting (2D) of the ground 4A2g term by spin-orbit coupling and of magnetic exchange interaction between the chromium atoms. The magnetic exchange is modelled as one of Ising or mean-field in type. The exchange is found to be quite small: J = -0.18(6) cm-1 if the Ising model is employed, and -0.03(1) cm-1 for the mean-field model. The model adopted for the exchange has a strong influence on the value of the parameter D obtained. When the Ising model is used D is deduced to be -0.28(9) cm-l; when the mean-field model is used D is -0.14(4) cm-l. The g-values deduced are in agreement with those from e.s.r. measurements at higher temperatures and do not depend on the exchange model. In any case, D is found to be sufficiently large that it must be considered in a polarized neutron diffraction experiment on the compound.

The Ground State in Cs2KFe(CN)6 From Single-Crystal Magnetic Properties

The single-crystal magnetic susceptibilities from 4.5 to 300 K, and the magnetizations at 4.5 K from 0.25 to 5 T, of Cs2KFe(CN)6 along a, b and c* are reported. The data are fitted well by a crystal field model with splitting of the ground-state 2T2g term of the hexacyanoferrate (III) ion. The three variable parameters of the model were the two representing the low-symmetry splitting of the t2g orbitals, and the effective reduction in the orbital angular momentum. Four other parameters were fixed at values known or estimated from other experiments on hexacyanoferrate (III) ions, including polarized neutron diffraction which determines the orientation of lower-symmetry crystal field components. The crystal field has only inversion symmetry with respect to the ligand axes, with a non-cubic component which is almost uniaxial with respect to the a,b,c * axis system.

Homology between proteins controlling Streptomyces fradiae tylosin resistance and ATP-binding transport

A tylosin(Ty)-producing strain of Streptomyces fradiae contains at least three genes, tlrA, tlrB, tlrC, specifying resistance to Ty (TyR). The complete nucleotide sequence of the TyR-encoding gene, tlrC, and the transcription start point of the gene were determined. The sequence contains an open reading frame coding for a protein of 548 amino acids (aa) with an Mr of 59129. The TlrC protein was identified by expression of the cloned gene by in vitro coupled transcription and translation in cell-free extracts derived from Streptomyces lividans. The N- and C-terminal halves of TlrC share extensive homology, suggesting that the protein evolved through tandem gene duplication. Each half of the deduced TlrC aa sequence also shows significant homology to numerous eukaryotic and prokaryotic membrane-associated, active-transport protein subunits. The homologous proteins include examples from the systems responsible for efflux of cytotoxic drugs from multidrug-resistant human cells and for export of hemolysin from Escherichia coli. The greatest similarity to TlrC is in regions containing the ATP-binding sites found in these proteins. These results suggest a role for the tlrC gene product as part of a multiple component, ATP-dependent transport system for the active excretion of Ty from the producing organism.