Identification and characterization of a heat shock protein 70 family member in channel catfish (Ictalurus punctatus)

We have determined the cDNA sequence of a member of the channel catfish heat shock protein 70 (CF Hsp70) family. This protein presumably functions as a molecular chaperone, as is characteristic of this family in other species. Channel catfish peripheral blood leukocytes exhibit a classical heat shock response, in that heat shock (37 degrees C) induces the expression of heat shock genes that are quiescent at normal temperatures (23 degrees C). It was observed that pre-existing synthesis of certain other molecules was suppressed (as evidenced by decreases in actin RNA upon heat shock). Similar trends were observed in mRNA expression for CF Hsp70 in two catfish non-leukocyte cell lines, channel catfish ovary and F59. However, three leukocyte cell lines constitutively expressed high levels of CF Hsp70 mRNA at optimal culture temperature (27 degrees C), whereas heat shock (37 degrees C) elicited only a modest induction of CF Hsp70 expression. Furthermore, continued investigation is warranted to determine whether the apparent upregulation of CF Hsp70 mRNA expression in the catfish long-term leukocyte cell lines is involved in the seemingly immortal phenotype of these cells.

Prevent Blindness America visual field screening study. The Prevent Blindness America Glaucoma Advisory Committee

PURPOSE

To assess the screening efficacy and practical use of two portable devices to detect moderate to severe visual field loss rapidly in population screening.

METHODS

Henson visual field analysis and Damato campimetry for glaucoma were performed in a healthy adult population, to determine false-positive rates; in established glaucoma patients and suspects, to determine false-negative rates; and in a general adult population, to assess practical use in actual screenings.

RESULTS

There were no false-positive test failures among the 82 normal subjects who completed the Henson two-step screening. Eighty of 83 normal subjects passed Damato campimetry, resulting in a false-positive rate of 3.6%. Among 83 glaucoma suspects and patients, the Henson test identified 49 (84%) of 58 subjects whose full-threshold fields from Humphrey perimetry were abnormal, 38 (97%) of 39 of whom had moderate to severe visual field loss. The Damato campimeter detected 55 (81%) of 68 subjects with any pathologic loss on full-threshold visual fields, 44 (92%) of 48 of whom had moderate to severe visual field loss. Among 1,278 subjects tested in general population screenings, 55 subjects (4.3%) failed either or both tests.

CONCLUSIONS

The Henson visual field analyzer can discriminate moderately to severely diseased from normal visual fields with high sensitivity and specificity. The Damato campimeter can reliably detect moderate to severe visual field loss with a tolerably low false-positive rate. To overcome the weakness of glaucoma screening by tonometry alone, some forms of visual field testing may be acceptably brief (cost effective) and accurate (sensitive and specific).

Initial clinical experience with the Ahmed Glaucoma Valve implant

PURPOSE

We studied the Ahmed Glaucoma Valve implant, an aqueous shunting device that has a unidirectional valve mechanism designed to prevent postoperative hypotony in eyes with intractable glaucoma.

METHODS

In this multicenter, prospective clinical trial, we studied 60 eyes (60 patients) with increased intraocular pressure or glaucoma that had not responded to medical treatment, laser photocoagulation, or previous glaucoma surgery, in which the Ahmed Glaucoma Valve implant was placed to decrease intraocular pressure.

RESULTS

Success was defined as intraocular pressure less than 22 mm Hg and greater than 4 mm Hg for two months or longer, intraocular pressure that was lowered by at least 20% from preoperative values (in eyes with preoperative intraocular pressures less than 22 mm Hg), and no additional glaucoma surgery or visually devastating complications. Cumulative probability of success at 12 months was 78%. Eight (13%) of 60 eyes had intraocular pressure less than 5 mm Hg the first postoperative day. Two other eyes had shallow anterior chambers, which required anterior chamber reformation. The major complications associated with the use of the valve were serous choroidal detachments in 13 eyes (22%), blockage of the tube in six eyes (10%), malposition of the tube in four eyes (7%), a suprachoroidal hemorrhage in one eye (2%), and corneal graft rejections in three (19%) of 16 eyes with corneal grafts.

CONCLUSIONS

Although the 12-month success with the Ahmed Glaucoma Valve implant is similar to that reported for other drainage devices, the complications associated with overfiltration in the immediate postoperative period appear to be less frequent than with other valved drainage devices. Randomized, prospective studies to compare the Ahmed Glaucoma Valve implant with other drainage devices are needed to make clinical comparisons of the different devices.

Treatment of nude mice with 4-amidinoindan -1- one2 '- amidinohydrazone, a new S-adenosylmethionine decarboxylase inhibitor, delays growth and inhibits metastasis of human melanoma cells

CGP 48664A (4-amidinoindan-1-one2'-amidinohydrazone) is a novel inhibitor of S-adenosyl-methionine decarboxylase (SAMDC), a key enzyme in the biosynthesis of polyamines, which are themselves essential for proliferation of mammalian cells. Seven different human melanoma cell lines were treated in vitro with CGP 48664A. High, intermediate and low levels of cytostasis were induced in four, one and two melanoma lines, respectively. This cytostasis was reversed by the addition of exogenous spermidine or spermine to the culture medium. The heterogeneous low metastatic (CGP 48664A-resistant) A375P cells and highly metastatic (CGP 48664A-sensitive) A375SM cells were implanted into the subcutis or injected intravenously into nude mice. Systemic daily administration of CGP 48664A significantly reduced the size of cutaneous lesions and the number of lung metastases in mice implanted with A375SM cells. No beneficial effects were found in mice injected with A375P cells. Drug activity was dose dependent, and maximal effects were observed when treatment began in mice with small tumour burdens. The data suggest that CGP 48664A is effective against melanoma metastasis in nude mice and that its activity should be tested in combination with other cytoreductive agents.

Extraction, PCR amplification and sequencing of mitochondrial DNA from human hair shafts

Techniques have been developed for extracting, amplifying and directly sequencing mitochondrial DNA (mtDNA) from human hair shafts. The hair shaft is ground in a glass micro-tissue grinder, and the DNA is extracted with organic solvent and purified by filtration. The filtrate subsequently provides the mtDNA template for the PCR. The two hypervariable segments of the mtDNA control region are amplified in four separate reactions. After a purification step to remove unincorporated PCR primers, amplified products are quantitated by capillary electrophoresis and subjected to cycle sequencing. The products are separated and analyzed on an automated DNA sequencer. The mtDNA sequences from the hair shaft match the mtDNA sequences from blood samples taken from the same donor.

Validation of mitochondrial DNA sequencing for forensic casework analysis

Two sets of studies were performed to evaluate the forensic utility of sequencing human mitochondrial DNA (mtDNA) derived from various tissues and amplified by the polymerase chain reaction (PCR). Sequencing was performed on a Perkin-Elmer/Applied Biosystems Division (PE/ABD) automated DNA sequencer (model 373A). The first set of experiments included typical validation studies that had previously been conducted on forensic DNA markers, such as: chemical contaminant effects on DNA from blood and semen and the effect of typing DNA extracted from body fluid samples deposited on various substrates. A second set of experiments was performed strictly on human hair shafts. These studies included typing mtDNA from hairs that were: (1) from different body areas, (2) chemically treated, (3) from deceased individuals, and (4) deliberately contaminated with various body fluids. The data confirm that PCR-based mtDNA typing by direct automated sequencing is a valid and reliable means of forensic identification.

cDNA sequences and organization of IgM heavy chain genes in two holostean fish

Immunoglobulin M heavy chain (mu) sequences of two holostean fish, the bowfin, Amia calva, and the longnose gar, Lepisosteus osseus, were amplified from spleen mRNA by RACE-PCR, cloned, and sequenced. Each mu chain showed the conserved four constant domain structure typical of a secreted mu chain. Southern blot analyses with specific heavy chain variable (VH) and constant (CH) region probes suggest that both fish possess an IgH locus that resembles that of the teleosts, amphibians, and mammals in its organization. The overall sequence similarity of gar and bowfin mu chains was 60% and 48% at the nucleotide and amino acid levels, respectively, while similarity to the mu chains of teleosts and elasmobranchs was lower. The bowfin mu chain possesses a distinctive proline-rich sequence at the C mu 1/C mu 2 boundary; a shorter proline-rich sequence is present at this position in the gar mu chain. Both gar and bowfin show, in their C mu 4 sequences, motifs that could serve as cryptic splice donor sites for the production of mRNA encoding the membrane-bound form of the mu chains, and the bowfin also shows a potential cryptic splice donor site in the C mu 3 exon.

Alternate pre-mRNA processing pathways in the production of membrane IgM heavy chains in holostean fish

A single gene encodes two forms of the IgM heavy chain (mu) in vertebrates: one (microseconds) present in serum as secreted IgM and the other (microns) as the antigen receptor form of IgM present on the B-lymphocyte membrane. The mRNAs encoding microseconds and microns are derived from a single primary transcript by alternate pathways of RNA processing. In all vertebrates so far examined, with the exception of teleosts, microns mRNA is produced by splicing the transmembrane (TM) encoding exon 1 into a cryptic donor site near the 3' end of the C mu 4 exon. In contrast, teleost species splice the TM exon 1 into the regular splice donor site at the 3' boundary of the C mu 3 exon. We have examined micron mRNAs in two species of primitive bony fish, the holostean bowfin and the longnose gar. These fish utilize both the C mu 3 to TM1 (teleost) pathway and the typical cryptic C mu 4 to TM1 pathway. In addition the bowfin possesses a cryptic splice donor site near the middle of C mu 3. This is used in the production of a third species of microns-encoding mRNA, but does not participate in the production of an alternate form of the microseconds mRNA. The structure and patterns of expression of their mu genes suggest that the gar and bowfin may be more closely related than implied by the current view of fish evolution.

An Ig heavy chain enhancer of the channel catfish Ictalurus punctatus: evolutionary conservation of function but not structure

The teleost fishes are among the earliest evolutionary lineages to have an Ig heavy chain (IgH) locus whose organization approximates that of mammals. To understand transcriptional control of the IgH locus in a teleost fish and to gain insight into the evolution of the control elements, the enhancer activity in the IgH locus of the channel catfish, Ictalurus punctatus, was investigated. Segments of the locus extending from upstream of the proximal JH gene to 2.5 kb downstream of the second transmembrane (TM2) exon of the mu gene were tested in transient transfection expression assays in murine myeloma and T cell lines, and in catfish B lymphoblastoid, monocyte-like, and putative T cell lines. In marked contrast to mammals, no enhancer activity was observed in the catfish JH to C mu intron, but strong enhancer activity (approaching that of the murine IgH intronic enhancer) was identified in a 1.8-kb segment that included the TM2 exon. This catfish enhancer was active in a B lineage-specific manner in both catfish and murine cells. It was not localized in a small core region, but appeared to contain multiple, dispersed cooperative elements rich in octamer- and mu E5-related motifs. Although the catfish IgH enhancer shares functional characteristics with the mammalian IgH intronic and 3' enhancers, its unusual organization does not permit any obvious inferences concerning evolutionary relationships between the catfish enhancer and any one of the murine IgH enhancers.

An Ig heavy chain enhancer of the channel catfish Ictalurus punctatus: evolutionary conservation of function but not structure

The teleost fishes are among the earliest evolutionary lineages to have an Ig heavy chain (IgH) locus whose organization approximates that of mammals. To understand transcriptional control of the IgH locus in a teleost fish and to gain insight into the evolution of the control elements, the enhancer activity in the IgH locus of the channel catfish, Ictalurus punctatus, was investigated. Segments of the locus extending from upstream of the proximal JH gene to 2.5 kb downstream of the second transmembrane (TM2) exon of the mu gene were tested in transient transfection expression assays in murine myeloma and T cell lines, and in catfish B lymphoblastoid, monocyte-like, and putative T cell lines. In marked contrast to mammals, no enhancer activity was observed in the catfish JH to C mu intron, but strong enhancer activity (approaching that of the murine IgH intronic enhancer) was identified in a 1.8-kb segment that included the TM2 exon. This catfish enhancer was active in a B lineage-specific manner in both catfish and murine cells. It was not localized in a small core region, but appeared to contain multiple, dispersed cooperative elements rich in octamer- and mu E5-related motifs. Although the catfish IgH enhancer shares functional characteristics with the mammalian IgH intronic and 3' enhancers, its unusual organization does not permit any obvious inferences concerning evolutionary relationships between the catfish enhancer and any one of the murine IgH enhancers.

Does the public understand the differences between ophthalmologists and optometrists?

Telephone interviews utilizing random digit dialing were conducted in Los Angeles County to assess the public's knowledge of differences between ophthalmologists and optometrists and to determine factors predictive of knowledge status. Knowledge status was determined by performance on a questionnaire specifically designed for this study. Using multiple logistic regression analysis for simultaneous evaluation of potentially predictive factors, higher education, history of prior eye examination as an adult, and history of prior or present contact lens or spectacle wear were associated with scoring as knowledgeable. Predicted probabilities of being knowledgeable and not knowledgeable were presented for all combinations of these predictive variables. Such information may be helpful in guiding public education campaigns regarding eye care.

In vivo modulation of macrophage tumoricidal activity by oral administration of the liposome-encapsulated macrophage activator CGP 19835A

The present study evaluated the in vivo biological activity of synthetic muramyl tripeptide, CGP 19835A, when encapsulated into phosphatidylcholine liposomes (POPC-19835A) and administered as an p.o. immunomodulator to BALB/c mice. Liposomes were rapidly absorbed in the intestine and reached the systemic circulation within 4 h. Alveolar macrophages harvested from the lungs of mice 24 h after a single p.o. feeding of POPC-19835A were tumoricidal toward syngeneic murine renal cell carcinoma target cells. Repeated daily feedings with POPC-19835A generated sustained activation of the alveolar macrophages. Activation of peritoneal macrophages to the tumoricidal state required at least three daily feedings of POPC-19835A. In vitro studies demonstrated the release of tumor necrosis factor alpha and interleukin 6 by macrophages activated by POPC-19835A in the presence of gamma-interferon. Interleukin 1 and nitric oxide were not induced in macrophages by this liposomal preparation. Daily administration of POPC-19835A after i.v. injection of renal cell carcinoma tumor in BALB/c mice inhibited the development of experimental lung metastasis and confirmed the potential role of long-term therapy with this new p.o. immunomodulator.

Analysis of the HUMTH01 allele frequencies in the Spanish population

Genetic marker typing based on DNA amplification by the polymerase chain reaction (PCR) increasingly is being employed in forensic casework and for paternity testing. The allele frequencies were determined using PCR for 120 unrelated Spanish Caucasians for the locus HUMTHOH1. Six alleles were observed, with frequencies ranging from 0.013 (allele 11) to 0.254 (allele 10). The observed heterozygosity was 75.8%, and the power of discrimination is 0.92. The genotype distribution meets Hardy-Weinberg expectations.

Quantitation of polymerase chain reaction products by capillary electrophoresis using laser fluorescence

In samples where the amount of DNA is limited, the polymerase chain reaction (PCR) can amplify specific regions of the DNA. A quantitative analysis of the PCR product would be desirable to ensure sufficient DNA is available for analysis. In this study, we examine the use of capillary electrophoresis (CE) with laser fluorescence detection for quantitation of PCR products. A coated open tubular capillary was used with a non-gel sieving buffer and a fluorescent intercalating dye to obtain results within 20 minutes. Using an internal standard, peak migration time was below 0.1% relative standard deviation (R.S.D.) with a peak area precision of 3% R.S.D. In comparison to quantitation by hybridization, (i.e., slot blot) and spectrophotometric analysis, capillary electrophoresis shows distinct advantages due to its ability to separate unincorporated primers and PCR byproducts from the targeted PCR product. The results demonstrate that CE can be used to monitor the quality and quantity of the PCR product.

Organ site-dependent expression of basic fibroblast growth factor in human renal cell carcinoma cells

We investigated the influence of organ microenvironment on the angiogenic phenotype in human renal cell carcinoma (HRCC) cells. HRCC line SN12C was established in vitro from a surgical specimen, and metastatic line SN12PM6 was isolated from a lung metastasis produced by parental cells implanted into the kidney of nude mice. SN12C (low metastasis) and SN12PM6 (high metastasis) cells were injected into the kidney or subcutis of nude mice. The kidney tumors were highly vascularized (as revealed by immunohistochemistry using antibodies against factor VIII), and metastatic, whereas the subcutaneous tumors were not. The expression of mRNA for basic fibroblast growth factor (bFGF) in kidney tumors was 10 to 20 times that found in subcutaneous tumors. Similar data were obtained at the protein level by using fluorescence activated cell sorting, immunohistochemistry, and enzyme-linked immunosorbent assay. bFGF was detected in the urine of mice with tumors in the kidney but not subcutaneous tumors. The level of bFGF in the serum of mice with kidney tumors was two to three times that in mice with subcutaneous tumors. The changes in bFGF expression in the tumors was transient. Collectively, these data indicate that the organ microenvironment can influence the expression level of bFGF in HRCC.

Free conjunctival patch for repair of persistent late bleb leak

In four patients, we repaired leaking blebs by using a new technique of excision of the cystic bleb and replacement with free conjunctival autograft. The leaks were repaired successfully, and bleb function was maintained in all four patients. This technique should be considered when surgical management of a leaking bleb is indicated.

Analysis of short tandem repeat (STR) HUMVWA in the Spanish population

Amplification by polymerase chain reaction (PCR) of variable number of tandem repeat (VNTR) loci and subsequent typing by electrophoresis and silver staining has become a useful tool for identity testing. One viable group of genetic markers amenable to amplification by PCR is the short tandem repeat (STR) loci. A horizontal discontinuous polyacrylamide gel electrophoresis (PAGE) method was used to type the amplified products of the STR HUMVWA. Typing for VWA of 120 unrelated Spanish Caucasians was done. Six alleles were observed with frequencies in the range 0.096-0.242. The genotype distribution meets Hardy-Weinberg expectations (0.25 < P < 0.50). The heterozygosity was 73.3% and the discrimination power (DP) 0.94. Simultaneously, in a small sample of families (n = 24) no new mutations could be found.

Sequential multiplex amplification (SMA) of genetic loci: a method for recovering template DNA for subsequent analyses of additional loci

A method called Sequential Multiplex Amplification (SMA) has been developed whereby a limited amount of DNA extracted from a sample can be reutilized for several single polymerase chain reaction (PCR) amplifications. The method involves recovery of genomic template DNA by microfiltration of PCR-amplified samples. Up to 5 different loci have been typed, each in a single system PCR-based assay, beginning with a test quantity of 5 ng template DNA. Genotypes of the DNA donors were compared with those obtained from individual amplifications and shown to be identical. This could be a useful technique for typing a number of loci from a limited amount of DNa and to recover template DNA from samples previously subjected to PCR. Obviously, when small quantities of template DNA are available, this technique can prove quite useful.

Effects of chronic phenylpropanolamine infusion and termination on body weight, food consumption and water consumption in rats

The present study determined the effect of chronic PPA infusion and withdrawal on weight regulation. Male Sprague-Dawley rats received PPA (0, 90 or 180 mg/kg) via miniosmotic pumps for 2 weeks. Body weight and food and water consumption were measured daily before, during, and for 2 weeks after PPA infusion. Additionally, body weight was measured once 6 weeks after the last day of drug administration. PPA infusion produced dose-dependent reductions in body weight and food consumption throughout drug administration. During the first week of PPA termination, food consumption returned to control levels; however, body weights of drug-treated animals remained below those of controls throughout the 6-week post-drug period. PPA depressed water intake during the first week of drug administration, but tolerance to this effect developed by the second week of administration. These results suggest chronic PPA infusion produces persistent appetite suppression and weight loss and that discontinuation of PPA does not result in hyperphagia or rapid weight gain. These findings may have clinical significance for the many individuals who wish to lose weight but have difficulty reducing intake without pharmacologic assistance.

The value of different screening techniques for glaucoma

The role of tonometry has been relegated from case finding to risk stratification, because intraocular pressure poorly differentiates between health and glaucomatous eyes. Led by the evidence that optic disc and retinal nerve-fiber layer change may precede glaucomatous visual field loss by several years, enormous efforts have been made to accurately measure these parameters for case definition; however, the wide variability in optic nerve head topography among the normal eyes, and the marginal quality of a substantial proportion of fundus photographs limit the usefulness of biomorphometry as a screening tool. Scanning laser ophthalmoscopy may potentially overcome the limitations of conventional photographic techniques for accurate biomorphometry, but this technology remains expensive. In light of the limitations of tonometry and biomorphometry in a general screening setting, the value of psychophysical testing has assumed an increasing importance. The low prevalence of glaucoma in an unselected adult population, combined with the lack of a valid screening technique, argues for a shift in focus from widespread population-based screening with a single test to case finding targeted at high-risk individuals.

Effects of family and marital psychotherapies: a meta-analysis

This meta-analysis of 163 randomized trials (including 59 dissertations) examines a number of questions not studied in previous syntheses. These include differences in outcome associated with different theoretical orientations, differences between marital and family therapies versus individual therapies, the clinical significance of therapy outcome, differences between marital versus family therapies in both outcomes and problems treated, and the effects of various substantive and methodological moderators of therapy outcome. The review concludes with some observations about the methodological status of this literature.

Development and characterization of channel catfish long term B cell lines

The establishment of channel catfish long term cloned B cell lines, the first such cell lines from ectothermic vertebrates, is described. These diploid cell lines were developed by in vitro LPS stimulation of B cells from normal channel catfish peripheral blood in the absence of overt attempts to transform or immortalize the cells. The resultant cell lines were cloned and maintained continuously in vitro for more than 12 mo without restimulation, feeder cells, or exogenous factors. Southern blot analyses of the parental cell lines revealed multiple mu-chain gene rearrangements, suggesting a polyclonal origin for the cell lines. Additional evidence for polyclonal development was provided by the demonstration that the parental cell lines transcribed mRNA for all of the six known channel catfish VH gene families. The characterization of several clonal cell lines revealed mRNA expression for both the secreted and membrane forms of the catfish mu-chain; however, the cloned cell lines each expressed only a single VH gene and analysis of the Ig H chain locus was consistent with allelic exclusion having occurred in these cells. Flow cytometry demonstrated that the cloned and uncloned cell lines produced both cytoplasmic and cell surface IgM. This IgM contained only one of the two L chain isotypes of the channel catfish, suggesting preferential L chain usage. Although these cells did not appear morphologically to be plasma cells, they secreted moderate levels of IgM in culture. These cell lines have considerable potential for addressing questions concerning the evolution of B cell function.

Development and characterization of channel catfish long term B cell lines

The establishment of channel catfish long term cloned B cell lines, the first such cell lines from ectothermic vertebrates, is described. These diploid cell lines were developed by in vitro LPS stimulation of B cells from normal channel catfish peripheral blood in the absence of overt attempts to transform or immortalize the cells. The resultant cell lines were cloned and maintained continuously in vitro for more than 12 mo without restimulation, feeder cells, or exogenous factors. Southern blot analyses of the parental cell lines revealed multiple mu-chain gene rearrangements, suggesting a polyclonal origin for the cell lines. Additional evidence for polyclonal development was provided by the demonstration that the parental cell lines transcribed mRNA for all of the six known channel catfish VH gene families. The characterization of several clonal cell lines revealed mRNA expression for both the secreted and membrane forms of the catfish mu-chain; however, the cloned cell lines each expressed only a single VH gene and analysis of the Ig H chain locus was consistent with allelic exclusion having occurred in these cells. Flow cytometry demonstrated that the cloned and uncloned cell lines produced both cytoplasmic and cell surface IgM. This IgM contained only one of the two L chain isotypes of the channel catfish, suggesting preferential L chain usage. Although these cells did not appear morphologically to be plasma cells, they secreted moderate levels of IgM in culture. These cell lines have considerable potential for addressing questions concerning the evolution of B cell function.

Molecular analysis of the glycoprotein C-negative phenotype of attenuated Marek's disease virus

Serial passage of oncogenic serotype 1 Marek's Disease virus (MDV) in cultured avian cells results in attenuation of viral oncogenicity and pathogenicity. Coincident with attenuation, expression of MDV glycoprotein C (gC) is significantly reduced. Regulation of MDV gC may have important implications for virus-host interactions and have important consequences in the process of viral attenuation. To investigate the mechanism by which MDV gC expression is reduced during attenuation of the very virulent serotype 1 MDV strain Md11, protein levels, gene structure, steady-state RNA levels, and transcription rates of MDV gC from oncogenic and attenuated isolates of Md11 were determined. Comparison of these data with similar studies on MDV proteins whose expression is not altered during attenuation indicates that reduced expression of MDV gC is directly related to reduction in transcription rate of the MDV gC gene in attenuated Md11. Reduced transcription rates and lack of any gross structural alterations in the attenuated MDV gC gene suggest that MDV regulatory protein(s) which interact with the MDV gC promoter are altered during attenuation of MDV strain Md11. This conclusion is supported by DNA sequence data which indicate that the promoters of oncogenic and attenuated Md11 gC genes are identical.