Early malnutrition followed by nutritional restoration lowers the conduction velocity and excitability of the corticospinal tract

The physiological sequelae of undernutrition were investigated in rats that were undernourished from day 1-21 and subsequently free-fed to 75 days of age. Population responses were recorded in the corticospinal tract following surface stimulation of the motor cortex, which activates corticospinal cells directly, and also indirectly via cortical synapses. The conduction velocity of the fastest corticospinal fibers in 15 malnourished rats was 16.9 m/s, significantly slower (P < 0.001) than the 20.0 m/s observed in 26 controls. In addition, the excitability of corticospinal neurons to direct stimulation was reduced as much as 67% in malnourished rats, while no effect on synaptic activation was observed. Our findings suggest that early malnutrition reduces the number of large fibers in the adult corticospinal tract. These results are discussed with respect to known morphological and behavioral effects of malnutrition in rats and their relevance to humans.

Molecular mobility of the Ca(2+)-deficient EF-hand of cardiac troponin C as revealed by fluorescence polarization of genetically inserted tryptophan

To probe attitudinal features of the Ca(2+)-deficient site (site I) in the Ca2+ switch of cardiac troponin C (cTnC), we have examined steady-state fluorescence emission and polarization of a Trp26 inserted in a recombinant cardiac TnC (cTnC3.W) and compared these with the properties of the Ca(2+)-competent site I in skeletal TnC (sTnC4.W). The Ca(2+)-induced fluorescence emission in cTnC3.W was a fraction (25-30%) of that in sTnC4.W, in agreement with previous observations on the Ca(2+)-deficient site incorporated in a cardiac/skeletal chimera c1/s.W [Gulati, J. & Rao, V. G. (1994) Biochemistry 33, 9052-9056]. Thus, the fractional quantum yield reflected intrinsic properties of the cardiac metal ion-deficient site I. Conversely, in sTnC-1.W, where the skeletal site I also was made Ca(2+)-deficient by D27-->A substitution, the Ca(2+)-induced quantum yield was lower than that in cTnC3.W. Nevertheless, similar steady-state fluorescence polarizations for Ca(2+)-saturated sTnC4.W and cTnC3.W indicated indistinguishable final conformations in the two activated TnC isoforms. In EGTA, the polarization parameter (PEGTA) of sTnC4.W is greater than that of cardiac TnC, and the cardiac PEGTA value is closer to the activated PCa. Comparison of the chimera c1/s.W with sTnC-1.W indicated that the differences in conformation of the site I Trp for the EGTA-treated cardiac/skeletal isoforms were due to the structural disparities in this region. This contention was further supported by examination of the chimera CBc1/s.W, where the cardiac EF-hand was altered by 27VLGA30-->DAD substitution. Polarization of the relaxed form was similar to that for sTnC4.W. These findings suggest that the relaxed conformation of the cardiac Ca2+ switch is more favorably predisposed to activation than the skeletal switch.

The number of amino acid residues in hydrophilic loops connecting transmembrane domains of the GABA transporter GAT-1 is critical for its function

Transporter proteins consist of multiple transmembrane domains connected by hydrophillic loops. As the importance of these loops in transport processes is poorly understood, we have studied this question using the cDNA coding for GAT-1, a Na+/Cl(-)-coupled gamma-aminobutyric acid transporter from rat brain. Deletions of randomly picked non-conserved single amino acids in the loops connecting helices 7 and 8 or 8 and 9 result in inactive transport upon expression in HeLa cells. However, transporters where these amino acids are replaced with glycine retain significant activity. The expression level of the inactive mutant transporters was similar to that of the wild-type, but one of these, delta Val-348, appears to be defectively targetted to the plasma membrane. Our data are compatible with the idea that a minimal length of the loops is required, presumably to enable the transmembrane domains to interact optimally with each other.

Production and quality of eggs from sex-linked imperfect albino (sal-s) and nonalbino (s+) hens kept under commercial conditions

The beneficial effects of the gene for imperfect albinism on egg production were investigated under commercial conditions. In one line (Line 8) but not in another (Line 3), hen-day egg production of albinos from 46 to 75 wk of age was higher than that of nonalbinos (76.1 vs 72.6%) resulting in higher overall hen-day (71.1 vs 69.3%, P < .08) and hen-housed (276.3 vs 263.6 eggs) egg production by albino hens. Egg production of Line 8 albinos was not different than that of one of two commercial strains (Strain A) included as a control (76.1 vs 75.6%, P > .05). In data from Lines 3 and 8 combined, sexual maturity of albinos was delayed by 3.0 d. Mortality was higher for albinos than nonalbinos (3.6 vs 1.8%) during the first 2 wk of brooding and lower for albinos (5.8 vs 8.9%) during the laying period. Eggs from albinos weighed less (53.8 vs 55.3 g), had smaller yolks (16.9 vs 17.6 g) and shells (5.16 vs 5.27 g), and firmer albumen (5.9 vs 5.6 mm). The results suggest that the gene produces beneficial effects on egg production under commercial conditions.

Disparate contributions of Tyr10 and Tyr109 to fluorescence intensity of rabbit skeletal muscle troponin C identified using a genetically engineered mutant

Intrinsic tyrosines, as monitored by fluorescence spectroscopy, are sensitive reporters of local, Ca(2+)-induced conformational changes in troponin C (TnC). Rabbit skeletal TnC contains two tyrosines (Y10 in the N-helix, and Y109 in site 3 in the C-terminal domain) in distinct microenvironments: their individual contributions to total fluorescence intensity are elucidated here utilizing bacterially synthesized rabbit skeletal TnC (sTnC4) and a genetically engineered variant, termed 109YF, lacking one of the tyrosines (Y109 replaced with F109). The steady-state fluorescence emission spectra following excitation at 280 nm were recorded in EGTA (Ca(2+)-free) and Ca(2+)-saturated (pCa4) solutions. For the wild-type sTnC4, pCa4 causes a significant (46%) increase in the peak fluorescence intensity over the value in EGTA. For the mutant 109YF, the EGTA fluorescence is only marginally affected (74% of the wild-type FEGTA), but interestingly the Ca2+ effect is completely suppressed (delta F = FpCa4-FEGTA = 2% of the wild-type value). These results indicate that the two tyrosines make disparate contributions to the fluorescence spectrum of wild-type sTnC, both in the presence and absence of Ca2+; whereas Y10 in the N-helix is dominant in Ca(2+)-free solution, Y109 is the sole contributor to the Ca2+ effect. Furthermore, to explain the biphasic fluorescence response of Y109 obtained during Ca2+ titrations, the findings yield the most unequivocal evidence that Ca(2+)-induced conformational changes in the trigger sites operating the contractile switch modify properties of the C-terminal sites in TnC pari passu.

The role of glycine (residue 89) in the central helix of EF-hand protein troponin-C exposed following amino-terminal alpha-helix deletion

Because an N-terminal alpha-helical (N-helix) arm and a KGK-triplet (residues 88KGK90) in the central helix of troponin-C (TnC) are missing in calmodulin, several recent studies have attempted to elucidate the structure-function correlations of these units. Presently, with a family of genetically manipulated derivatives especially developed for this study and tested on permeabilized isolated single skeletal muscle fiber segments, we explored the specificities of the amino acid residues within the N-helix and the KGK-triplet in TnC. Noticeably, the amino acid compositions vary between the N-helices of the cardiac and skeletal TnC isoforms. On the other hand, the KGK-triplet is located similarly in both TnC isoforms. We previously indicated that deletion of the N-helix (mutant delta Nt) diminishes the tension obtained on activation with maximal calcium, but the contractile function is revived by the superimposed deletion of the 88KGK90-triplet (mutant delta Nt delta KGK; see Gulati J, Babu A, Su H, Zhang YF, 1993, J Biol Chem 268:11685-11690). Using this functional test, we find that replacement of Gly-89 with a Leu or an Ala could also overcome the contractile defect associated with N-helix deletion. On the other hand, replacement of the skeletal TnC N-helix with cardiac type N-helix was unable to restore contractile function. The findings indicate a destabilizing influence of Gly-89 residue in skeletal TnC and suggest that the N-terminal arm in normal TnC serves to moderate this effect. Moreover, specificity of the N-helix between cardiac and skeletal TnCs raises the possibility that resultant structural disparities are also important for the functional distinctions of the TnC isoforms.

Cardiac myocyte function and left ventricular strains after brief ischemia and reperfusion in rabbits

BACKGROUND

After a brief episode of ischemia, myocardial function may be depressed for prolonged periods despite reperfusion. The mechanisms of postischemic dysfunction differ depending on the experimental model. Regional ischemia and reperfusion in the intact animal provide a clinically relevant model, but experimental variables are difficult to control. Experimental conditions can be well controlled in isolated cardiac muscle and myocyte preparations, but these models are limited by the assumptions used to mimic ischemia and reperfusion. This study combines the unique advantages of both preparations. We characterized in vivo alterations in regional two-dimensional finite strains with ischemia and reperfusion produced in the intact animal, then isolated cardiac myocytes from the region with postischemic dysfunction to characterize in vitro function of postischemic myocytes.

METHODS AND RESULTS

In seven anesthetized rabbits, three piezoelectric crystals were inserted in a triangular array to measure two-dimensional finite strains around the large coronary artery in the left ventricular anterior free wall. After 15 minutes of ischemia and reperfusion, strains were depressed at a stable level approximately 30% to 40% below control values between 1 and 6 hours after reperfusion. The direction of maximal shortening deformations was midway between circumferential and longitudinal directions during control and did not shift after reperfusion. In a second group of five rabbits, cardiac myocytes were isolated from the region with postischemic dysfunction after 15 minutes of ischemia and 45 minutes of reperfusion. We compared in vitro function in 45 postischemic myocytes with 48 cardiac myocytes isolated from five normal rabbits. Each rabbit (postischemic and control) contributed 9 +/- 1 (SD) myocytes to the study. All myocytes were studied within 1 hour after myocyte isolation (approximately 3 to 5 hours after reperfusion for postischemic myocytes). Myocytes were stimulated at 0.5 Hz and perfused with 2 mmol/L [Ca2+] Tyrode's solution to measure unloaded cell shortening. There was significantly less shortening in postischemic myocytes (12.4 +/- 2.1%) than control myocytes (16.2 +/- 1.2%). Maximal cell length (Lmax) was significantly longer in postischemic (134 +/- 7 microns) than control myocytes (122 +/- 7 microns), as was minimum cell length (Lmin) (118 +/- 8 versus 103 +/- 9 microns, respectively). The duration of shortening (time from stimulation to Lmin) was significantly shorter in postischemic (279 +/- 56 milliseconds) than control myocytes (405 +/- 44 milliseconds). Peak rates of cell shortening (-dL/dt) and lengthening (+dL/dt) did not differ.

CONCLUSIONS

In rabbits, 15 minutes of ischemia produced a stable depression in finite strains for 1 to 6 hours after reperfusion, with shortening deformations reduced by approximately 30% to 40% without a shift in direction. Cardiac myocytes isolated from postischemic myocardium display functional impairments in vitro similar to those measured in vivo, with an approximately 25% reduction in unloaded myocyte shortening and decreased contraction duration. This indicates that ischemia and reperfusion induce intrinsic impairments in contractility independently of external loading conditions. This model may be useful for examining cellular mechanisms of postischemic myocardial dysfunction.

Development of polyclonal antibodies and evaluation of a sensitive radioimmunoassay for detection and measurement of synaptophysin

Polyclonal antibodies directed towards synaptophysin were raised against a synthesised peptide corresponding to amino acids 246 to 260 of the human synaptophysin sequence. The antibodies, when applied for immunocytochemical staining, showed a staining pattern identical to that of the commercially available monoclonal antibody SY-38. A radioimmunoassay for measurements of synaptophysin was developed using these antibodies and the peptide as standard and tracer. The radioimmunoassay was used for optimising the conditions for purification of synaptophysin from rat brain. No synaptophysin was detected in blood plasma in humans, not even during an embolisation treatment of tumour metastases in the liver, which induced tumour cell necrosis, in a patient with carcinoid tumours. By radioimmunoassay, synaptophysin was detected in cell homogenate from the PC-12 (160 ng/mg) and LCC-18 (40 ng/mg) cell lines and in the cell culture media. In the LCC-18 cell line the synaptophysin immunoreactivity was found in the plasma membrane, and the presence of synaptophysin was confirmed both by radioimmunoassay measurements and by the Northern blot technique. These data indicate that measurements of synaptophysin using this radioimmunoassay are reliable and that the assay can serve as a useful tool in further explorations of the biological effects of synaptophysin.

The human homologue of the retroviral oncogene qin maps to chromosome 14q13

Chromosomal mapping of the human QIN gene (renamed FKH2 by the Human Genome Organization Nomenclature Committee) was initially accomplished by correlation of the presence of the QIN locus with specific chromosome regions in a rodent-human hybrid panel. This analysis revealed that the human QIN gene maps to chromosome region 14q11.2-->14q32, between the TCR and IGH loci. Further analysis by fluorescence in situ hybridization techniques with a human QIN genomic clone refined the human QIN gene localization to 14q13.

A poliovirus hybrid expressing a neutralization epitope from the major outer membrane protein of Chlamydia trachomatis is highly immunogenic

Trachoma and sexually transmitted diseases caused by Chlamydia trachomatis are major health problems worldwide. Epitopes on the major outer membrane protein (MOMP) of C. trachomatis have been identified as important targets for the development of vaccines. In order to examine the immunogenicity of a recombinant vector expressing a chlamydial epitope, a poliovirus hybrid was constructed in which part of neutralization antigenic site I of poliovirus type 1 Mahoney (PV1-M) was replaced by a sequence from variable domain I of the MOMP of C. trachomatis serovar A. The chlamydial sequence included the neutralization epitope VAGLEK. This hybrid was viable, grew very well compared with PV1-M, and expressed both poliovirus and chlamydial antigenic determinants. When inoculated into rabbits, this hybrid was highly immunogenic, inducing a strong response against both PV1-M and C. trachomatis serovar A. Antichlamydia titers were 10- to 100-fold higher than the titers induced by equimolar amounts of either purified MOMP or a synthetic peptide expressing the VAGLEK epitope. Furthermore, rabbit antisera raised against this hybrid neutralized chlamydial infectivity both in vitro, for hamster kidney cells, and passively in vivo, for conjunctival epithelia of cynomolgus monkeys. Because poliovirus infection induces a strong mucosal immune response in primates and humans, these results indicate that poliovirus-chlamydia hybrids could become powerful tools for the study of mucosal immunity to chlamydial infection and for the development of recombinant chlamydial vaccines.

Critical minimum length of the central helix in troponin C for the Ca2+ switch in muscular contraction

In the troponin C (TnC) dumbbell, the NH2- and COOH-terminal lobes are well delineated, but the role of the central helix and especially the function of its long length remain doubtful. To study this, we used a cDNA construct encoding rabbit fast-twitch muscle TnC, comprising multiple restriction sequences to facilitate mutagenesis (Babu, A., Su, H., Ryu, Y. & Gulati, J. (1992) J. Biol. Chem. 267, 15469-15474). Systematically, we have deleted 3-12 amino acid residues from the central helix and examined their effects in maximally activated skinned muscle fibers. Limiting the deletions to 7 amino acid residues manifested little change in maximal force development (Sheng, Z., Francois, J. M., Hitchcock, S. E. & Potter, J. D. (1991) J. Biol. Chem. 266, 5711-5715). However, with further deletions, we now find that contractility was inhibited pari passu; by 12 deletions, the inhibition was complete. The critical minimum length for the central helix is thereby estimated as 27 A. The Ca2+ binding capacity (4 mol of Ca2+/mol of protein) as well as the structural characteristics (alpha-helicity by CD measurements and the fluorescence emitted by Tyr-109) indicated a well preserved global conformation of the short mutant. However, surprisingly, two of these short mutants filled each TnC slot under highly specific superloading conditions: one short molecule was taken up in EGTA solution, and the second molecule was captured and retained with Ca2+. They also rescued the contractile switch, evidently in a bimolecular reaction. Another short variant (putative skeletal fast muscle TnC-I-II), in which the NH2-terminal Ca(2+)-binding sites were incapacitated, failed to respond to superloading, indicating that sites III and IV could not substitute for sites I and II. The results suggest that a critical role of the central helix linker in TnC is to keep the two lobes optimally apart, evidently in proximity of their respective target sites on troponin I in the fiber.

Vasoactive intestinal peptide stimulates the growth of rat hepatoma cells in vitro

Using tetrazolium colorimetric assay (MTT assay) and cell counting methods, the effect of vasoactive intestinal peptide (VIP) on the growth of cultured rat hepatoma FSK-7902 cells was investigated. The results showed that VIP obviously stimulated the proliferation of the rat hepatoma cells. The growth promoting effect increased with VIP concentration. Exposure to VIP for 12 h followed by removal of the peptide resulted in sustained growth promotion for several days.

Workshop on in vitro neutralization of Chlamydia trachomatis: summary of proceedings

A task force evaluated an in vitro antibody-mediated chlamydial neutralization assay for its utility as a method to assess functional correlates of antibody responses to Chlamydia trachomatis. Two monoclonal antibodies that recognize different major outer membrane protein (MOMP) epitopes for a C. trachomatis serovar B strain exhibit good in vitro neutralizing activity, with a maximum of 90% neutralization. Calculations based on the 50% neutralization point indicated that 100% neutralization could theoretically be achieved when only 10% of the MOMP molecules bound antibody. Monoclonal antibodies that recognized either a heterologous MOMP or the genus-specific chlamydial lipopolysaccharide did not produce neutralizing activity. The standardized assay will be useful to establish if in vitro neutralizing antibody responses are predictive of protective immunity and will aid in defining chlamydial antigens and epitopes that may be attractive vaccine candidates.

Identification of the regions conferring calmodulin-like properties to troponin C

The structural and functional correlations between troponin C (TnC) and calmodulin (CaM) were investigated by mutagenizing a synthetic cDNA coding rabbit skeletal muscle TnC. Compared with TnC, calmodulin lacks the N-terminal alpha-helical arm (N-helix), and its central helix is shorter due to the absence of 88KGK90 residues. Deleting both regions concomitantly (delta Nt delta KGK) elicited CaM-like regulation as tested (i) by smooth muscle contractility (maximal tension = 80 +/- 5% Po of control) and (ii) by the activation of phosphodiesterase (Vmax = 75 +/- 2% of control). The Ca(2+)-binding capacity of the mutant and the effect of the mutant on maximally Ca(2+)-activated tension of skinned rabbit psoas muscle fibers were both conserved. Furthermore, in the linker region of the central helix, replacing the TnC-characteristic 85EDAKGK90 successive residues with CaM-specific DTD residues generated a highly effective CaM mimic (Vmax = 96 +/- 2%) whether or not the N-helix was also retained. Apparent KD values (i.e. concentrations for half-maximal response) for the successful mutants were similar to each other but about 200-fold higher than that for CaM. A part of the alpha-helical linker region in CaM may unfold and bend to promote multiplicity of target interaction using all four hands (Ikura, M., Clore, G. M., Gronenborn, A. M., Zhu, G., Klee, C. B., and Bax, A. (1992) Science 256, 632-638; Meador, W. E., Means, A. R., and Quiocho, F. A. (1992) Science 257, 1251-1255). In contrast, our results suggest that the TnC central helix evolved to be less pliable by the combined influences of 85EDAKGK90 residues and the alpha-helical extension in N terminus, thereby keeping the N-terminal hands well separated from their C-terminal counterparts.

Use of gene fusions of the structural gene sdaA to purify L-serine deaminase 1 from Escherichia coli K-12

The purification by affinity chromatography of beta-galactosidase from strains carrying sdaA/lacZ gene fusions results in the copurification of L-serine deaminase 1. We conclude that sdaA is the structural gene for the latter enzyme. The purified L-serine deaminase 1 obtained after collagenase treatment of an sdaA-collagen-lacZ fusion differs from the native enzyme by the addition of several amino acids at the C-terminal. Like the enzyme in crude extracts, this purified enzyme is catalytically inactive, and is activated by incubation with iron and dithiothreitol.

The mechanism of Ca(2+)-coordination in the EF-hand of TnC, by cassette mutagenesis

Genetic engineering of TnC and skinned fiber physiology on rabbit psoas muscle are combined to study the mechanisms of Ca(2+)-binding in the EF-hand in TnC. Of the six coordinating positions (X,Y,Z,-Y,-X & -Z) for Ca(2+)-binding in the loop, the X position is invariably occupied by an aspartate, and the -Z position by a glutamate. X-ray analysis has indicated that both oxygen atoms of the beta-carboxylate in aspartate (in X) are extensively hydrogen bonded to other residues in the loop. When this aspartate in site II was replaced by a glutamate (gamma-carboxylate), Ca(2+)-binding was annihilated, and the mutant was unable to regulate force development in the fiber. Similarly, glutamate for aspartate exchange in the -Z position of site I also inactivated the site as well as its function in skinned fiber. Mutations in the Y position indicated that a glutamate was unacceptable in place of aspartate but that an asparagine was acceptable. The Ca(2+)-sensitivity with asparagine was also similar to that of the wild type. The study indicates a powerful approach for defining the physicochemical principles governing Ca-coordination and sensitivity in Ca-binding proteins. Furthermore, by comparison with findings on chemically synthesized peptides, the results show that behavior of the EF-hand in TnC is modified by quaternary structure of the molecule.

Immunogenicity of a synthetic oligopeptide corresponding to antigenically common T-helper and B-cell neutralizing epitopes of the major outer membrane protein of Chlamydia trachomatis

Sexually transmitted diseases (STDs) caused by Chlamydia trachomatis are an important public health problem and a vaccine to prevent or control these diseases is badly needed. The major outer membrane protein (MOMP) is the principal candidate antigen for the development of subunit vaccine against chlamydial STDs. The immunogenicity of a synthetic oligopeptide, termed A8-VDIV, corresponding to MOMP sequences containing both C. trachomatis species common T-helper (A8) and B-cell (VDIV) epitopes was studied in mice and non-human primates. Six of eight H-2 congenic mouse strains immunized with peptide A8-VDIV produced high-titre IgG antibodies against the VDIV B-cell portion of the oligopeptide. Fine mapping of the anti-peptide antibodies by pepscan ELISA showed that each of the responding mouse strains made antibodies reactive with a species-common septmeric neutralizing epitope 298LNPTIAG304 contained in the VDIV sequence. The mouse anti-peptide antibodies reacted with intact C. trachomatis elementary bodies (EBs) by ELISA and neutralized chlamydial infectivity for cultured eukaryotic cells with sub-species specificity. Three cynomolgus monkeys were immunized with peptide A8-VDIV and their IgG antibody responses were similarly studied. All three monkeys produced IgG antibodies which reacted with the VDIV peptide and which recognized the species-common LNPTIAG neutralizing site within the VDIV sequence. Monkey anti-peptide antibodies bound to intact C. trachomatis EBs and were neutralizing in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Identification of the transcriptional unit, structural organization, and promoter sequence of the human sex-determining region Y (SRY) gene, using a reverse genetic approach

Using a simple strategy involving cosmid-mediated gene transfer, cDNA library construction, and molecular characterization techniques, we have determined the transcriptional unit, structural organization, and promoter sequence of the human sex-determining region Y (SRY) gene, the putative testis-determining factor (TDF) gene on the human Y chromosome. By this approach, a recombinant cosmid harboring the human SRY sequence was isolated and transfected to appropriate tissue-cultured cells. Recombinant cDNA clones were isolated from a cDNA library constructed from poly (A) + RNA of the transfected cells. Comparative studies between the respective cDNAs and the genomic cosmid have provided information regarding the organization of the SRY gene and its mRNAs. The results indicate that the human SRY gene is an intronless gene, produces transcripts of 1.1 kb, and possesses promoter activities in the transfected cells at approximately 310 bp of its upstream sequences.

Functional delineation of the Ca(2+)-deficient EF-hand in cardiac muscle, with genetically engineered cardiac-skeletal chimeric troponin C

Cardiac and fast skeletal isoforms of TnC each comprise four putative EF-hand (helix-loop-helix) motifs as potential Ca(2+)-binding sites (sites 1-4), except that site 1 in cardiac TnC is deficient in Ca2+ coordination. In skeletal TnC, the N-terminal sites 1 and 2 are both essential for the trigger mechanism of the contraction switch. However, the mechanism in cardiac muscle is unsettled; it is obscure whether the cardiac site 1 is functionally inert due to calcium deficiency and consequently site 2 is the lone trigger site, or whether sites 1 and 2 perform interactively despite the impairment. These possibilities were addressed by mutagenizing site 1 in skeletal TnC to mimic the cardiac response. In one mutant (STnC-1), two selected Ca(2+)-ligands were abolished. In another (C1/S chimera), 41 N-terminal residues from cardiac TnC were spliced to STnC. The Ca(2+)-binding capacities as well as skinned fiber responses were measured. The STnC-1 derivative failed to switch on contraction. In contrast, the chimeric construct expressed close to full contractile potential in myocardium (74 +/- 3% Po; Po = maximal tension) and also the manifest cardiac phenotype. By devising supplemental chimeric constructs, cardiac-type N-terminal overhang together with cardiac-type EF-hand for site 1 both were found essential for the phenotype. We conclude that cardiac TnC site 1 is actively engaged in the trigger mechanism and in fact dominates the phenotype despite the inability to chelate Ca2+. The N-terminal overhang also participates in this mechanism, which is a novel finding. The conclusion that a non-chelating site functions interactively with a proximal site in cardiac TnC may have wider significance, inasmuch as similar pairings of disparate EF-hands are of common occurrence.

Repression of liver-specific hepatitis B virus enhancer 2 activity by adenovirus E1A proteins

Two regions of the hepatitis B virus (HBV) genome have been shown to display properties of a transcriptional enhancer. Enhancer 1 is active in most hepatoma lines examined as well as in some non-hepatocyte-derived cell lines. In contrast, enhancer 2 activity is strictly liver specific. In this study, we show that adenovirus E1A expression in the highly differentiated human hepatoma line Huh6 strongly inhibits HBV enhancer 2-stimulated transcription while having no effect on HBV enhancer 1 activity. A sequence motif in HBV enhancer 2 which is essential for its enhancer function is the target for E1A-mediated repression. The repression of HBV enhancer 2 activity is mediated through the N-terminal region of the E1A proteins known to bind a 300-kDa cellular protein. Our results suggest that HBV enhancer function may be modulated by a cellular mechanism similar to E1A-mediated transcriptional repression.

Demonstration of a stage-specific expression of the ZFY protein in fetal mouse testis using anti-peptide antibodies

The zinc finger Y (Zfy) gene is located on the Y chromosome of all placental mammals. Although it is phylogenetically conserved and is expressed in mouse fetal testis, it is not the sex determining Y (Tdy) gene. To address the possible function of the Zfy gene in mice, the distribution of Zfy protein in fetal mice was investigated by immunocytochemical staining using several specific antisera against synthetic peptides of the mouse Zfy protein. Analysis of various fetal tissues at different embryonic stages demonstrated a specific staining only in fetal testis. In particular, reactive protein was initially observed in male fetal gonads at day 11.5 postcoitum (p.c.). The immuno-staining intensified in fetal testes at day 12 and 12.5 p.c., decreased drastically in those at day 13 and 14 p.c. and became undetectable in those at day 15 p.c. and beyond. The reactive molecules were distributed mostly within the seminiferous tubules of the embryonic testis. The present observations confirm the previous findings with RT-PCR analysis and indicate that Zfy or Zfy-like protein is expressed in stage-specific manner during early testis differentiation. Its location in the seminiferous tubules suggests a possible role in early germ cell development.