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C C Yu

Publications and source records attributed to C C Yu.

At least 19 recordsLinked to original sources
PubMed2001

Protein phosphatase inhibitor cantharidin inhibits steroidogenesis and steroidogenic acute regulatory protein expression in cultured rat preovulatory follicles.

The effect of cantharidin, a natural toxicant of blister beetles and a strong inhibitor of protein phosphatases types 1 and 2A, on luteinizing hormone (LH)-induced synthesis of steroidogenic acute regulatory (StAR) protein was studied in a serum-free culture of preovulatory follicles. StAR protein is a steroidogenic tissue-specific, hormone-induced, rapidly synthesized protein previously shown to be involved in the acute regulation of steroidogenesis, probably by promoting the transfer of cholesterol to the inner mitochondrial membrane and the cytochrome P450 side-chain cleavage (P450scc) enzyme. Treatment of preovulatory follicles dissected from ovaries of immature rats primed with pregnant mares' serum gonadotropin (10 IU) with LH for 24 h resulted in a dose-dependent increase in the level of StAR protein that reached a maximum at 100 ng LH/ml. This increase was associated with an increase in progesterone production. Treatment of follicles with increasing concentrations (10 - 1000 ng/ml) of cantharidin suppresssed LH (100 ng/ml)-induced StAR protein levels and progesterone production in a dose-dependent manner. The amount of P450scc protein and the conversion of 22R-hydroxycholesterol to progesterone were not affected by cantharidin. This indicates that cantharidin did not interfere with the activity of P450scc. Cantharidin also decreased StAR protein levels and progesterone production induced by the adenylate cyclase activator forskolin (10(-5) M) or a cAMP analog 8-Br-cAMP (0.5 mM). These results demonstrate that cantharidin inhibits the LH-induced StAR protein levels, and, thus, suggest that phosphoprotein phosphatase activity is required for the cAMP-protein kinase A-stimulated steroidogenic activity of the preovulatory follicle.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2001

Dexamethasone enhances follicle stimulating hormone-induced P450scc mRNA expression and progesterone production in pig granulosa cells.

The effect of dexamethasone on follicle-stimulating hormone (FSH)-stimulated expression of cholesterol side-chain cleavage (P450scc) enzyme and production of progesterone by ovarian granulosa cells was studied in vitro. Granulosa cells from 3- to 5-mm pig antral follicles were cultured for 48 h in the presence or absence of FSH and/or dexamethasone. Treatment with FSH resulted in a dose-dependent increase in the level of P450scc mRNA that reached a submaximum at 100 ng FSH/ml. This increase was associated with an increase in progesterone production. Treatment of the cells with increasing concentrations (10(-9)-10(-6) M) of dexamethasone for 48 h increased constitutive and potentiated FSH-stimulated P450scc mRNA levels and progesterone production in a dose-dependent manner. Increasing duration (12-48 h) of treatment with dexamethasone (100 nM) led to a time-dependent increase in basal and FSH-stimulated progesteorne production, achieving statistical significance by 48 and 24 h, respectively. Dexamethasone also increased P450scc mRNA level and progesterone production induced by the adenylate cyclase activator forskolin (10 microM) or a cAMP analog 8-Br-cAMP (1 mM). The effects of dexamethasone on FSH-induced progesterone production were blocked by cotreatment of the cells with glucocorticoid receptor antagonist RU-486. These results demonstrate that dexamethasone potentiates FSH actions on steroidoogenesis in the pig ovary. Possible mechanisms for this potentiation include the ability of dexamethasone to stimulate P450scc gene expression.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed2001

Telomerase is regulated by protein kinase C-zeta in human nasopharyngeal cancer cells.

Telomerase, a specialized ribonucleoprotein reverse transcriptase that directs the synthesis of telomeric DNA, is repressed in normal human somatic cells, but is activated in most cancers. Little is known concerning how telomerase activity is activated and maintained in cancer cells. We have shown previously that inhibition of protein kinase C (PKC) decreases the telomerase activity of human nasopharyngeal carcinoma (NPC) cells. Here, we provide evidence that the decrease of telomerase activity by PKC inhibition is not mediated by transcriptional down-regulation of hTERT, the catalytic protein of human telomerase. In vitro phosphorylation studies revealed that exogenous addition of PKC-alpha, -betaI, -delta or -zeta led to restoration of telomerase activity in the crude extracts of PKC-inhibited NPC cells. However, depletion of PKC-alpha and -betaI in vivo had no detectable effect on the telomerase activity of NPC cells. Using antisense oligonucleotides against individual PKC isotypes, we observed that telomerase activity was inhibited only by the antisense oligonucleotide against PKC-zeta but not by those against PKC-alpha, -betaI or -delta. Taken together, these data demonstrate that PKC participates in the regulation of telomerase activity by direct or indirect phosphorylation of telomerase proteins, and that PKC-zeta is the PKC isotype that functions in vivo in the NPC cells.

Base Sequence↗
PubMed2001

Environmental lead exposure and progressive renal insufficiency.

BACKGROUND: Several recent studies show that serum creatinine level or creatinine clearance is inversely associated with blood lead levels. However, the studies did not allow direct inferences about causality. OBJECTIVE: To evaluate the relation between body lead burden (BLB) and progressive renal insufficiency in patients without previous heavy lead exposure. DESIGN: A prospective, longitudinal study with a controlled clinical trial. PATIENTS: One hundred ten patients with chronic renal insufficiency (serum creatinine level, 133-354 micromol/L [1.5-4.0 mg/dL]) and normal BLB (EDTA mobilization tests, <600 microg per 72-hour urine collection) and without a history of previous heavy lead exposure were divided into 2 groups according to BLB: the high-normal BLB group (BLB > or =80 microg and <600 microg) and the low BLB group (BLB <80 microg). Patients were prospectively followed up for 2 years. MAIN OUTCOME MEASURES: The primary outcome was a 1.5 times increase in the initial creatinine level. The secondary outcome was a change over time in the value of creatinine clearance. At the end of follow-up, a 3-month clinical trial with chelation therapy for patients with high-normal BLB was performed to clarify the role of environmental lead exposure in progressive renal insufficiency. RESULTS: Fifteen patients (14 in the high-normal BLB group and 1 in the low BLB group) reached the primary outcome within 24 months. Renal outcome was significantly better in the low BLB group (P<.001). From month 12 to month 24, renal function of high-normal BLB patients had a greater rate of progressive renal insufficiency than that of low BLB patients. In the Cox multivariate regression analysis, BLB was the most important risk factor for determining the progression of renal insufficiency. After chelation therapy, significant improvement in renal function was noted. In addition, the effect of improving renal function lasted for more than 12 months in these patients. CONCLUSIONS: Long-term low-level environmental lead exposure may subtly affect progressive renal insufficiency in the general population. Progressive renal insufficiency may be improved for at least 1 year after lead chelating therapy. Further investigations are needed to clarify this observation.

Adolescent↗
PubMed2001

Lupus-like kidney disease in mice deficient in the Src family tyrosine kinases Lyn and Fyn.

Systemic lupus erythematosus (SLE) is an autoimmune disease whose cause is poorly understood. Mice rendered deficient in specific genes have served as useful animal models in deciphering the genetic control of the disease [1]. We [2] and others [3, 4] previously demonstrated that mice deficient in the Src family tyrosine kinase Lyn developed a mild lupus-like disease with high survival rates. During the course of investigating the functional interaction of Src family kinases, we generated a mouse strain deficient in both Lyn and Fyn. The double-mutant mice died at relatively young ages and developed a severe lupus-like kidney disease. Unlike the double-mutant mice, single mutants deficient in either Lyn or Fyn lived longer and had distinct subsets of the symptoms found in the former. Lyn deficiency led to high levels of autoantibody production and glomerulonephritis, as previously reported [2--4], whereas loss of Fyn contributed to proteinuria by a B and T lymphocyte-independent mechanism. Our data suggest that the severe kidney disease in the double-mutant mice results from a combination of immunological and kidney-intrinsic defects. This new animal model may be informative about the causes of human SLE.

Animals↗
PubMed2001

Fendiline, an anti-anginal drug, increases intracellular Ca2+ in PC3 human prostate cancer cells.

BACKGROUND: The effects of the anti-anginal drug fendiline on intracellular Ca2+ concentrations ([Ca2+]i) in human PC3 prostate cancer cells were examined. METHODS: [Ca2+]i was measured using the fluorescent dye fura-2. RESULTS: Fendiline (0.5-100 microM) increased [Ca2+]i in a concentration-dependent manner. Ca2+ removal partly inhibited the Ca2+ signals. In Ca2+-free medium, pretreatment with 100 microM fendiline inhibited most of the [Ca2+]i increase induced by 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor), and pretreatment with thapsigargin abolished the fendiline-induced [Ca2+]i increases. Adding 3 mM Ca2+ increased [Ca2+]i in cells pretreated with 0.5-200 microM fendiline in Ca2+-free medium. Pretreatment with 1 microM U73122 to block the formation of inositol-1.4.5-trisphosphate (IP3) did not alter fendiline-induced internal Ca2+ release. CONCLUSIONS: The anti-anginal drug fendiline induced internal Ca2+ release and external Ca2+ entry. Because prolonged increases in [Ca2+]i may lead to cell injury and death, the long-term effect of fendiline on the function of prostate cancer cells should be investigated.

Adenosine Triphosphate↗
PubMed2001

Lead chelation therapy and urate excretion in patients with chronic renal diseases and gout.

BACKGROUND: It is known that chronic renal insufficiency (CRI) patients with gout may have subtle lead poisoning. In addition, gout episodes frequently aggravate progressive renal insufficiency because of the use of nephrotoxic drugs and urate deposition. Our study was arranged to evaluate the causal effect of environmental lead exposure on urate excretion in CRI patients. METHODS: A cross-section study and a randomized, controlled trial were performed. Initially, 101 patients with CRI and without a history of previous lead exposure received ethylenediaminetetraacetic acid mobilization tests to assess body lead stores (BLS). Then, a clinical trial was performed; 30 CRI patients with gout and high-normal BLS and the changes of urate excretion in these patients were compared before and after lead chelating therapy. The treated group received four-week chelating therapy, and the control group received a placebo therapy. RESULTS: The BLS of patients with CRI and gout was higher than that of patients with CRI only, and none had subtle lead poisoning. The BLS, not the blood lead level (BLL), significantly correlated to indices of urate excretion in all CRI patients after related factors were adjusted. In addition, after lead chelating therapy, urate clearance markedly improved after a reduction of the BLS of patients with CRI and gout (study group 67.9 +/- 80.0% vs. control group 1.2 +/- 34.0%, P = 0.0056). CONCLUSION: Our findings suggest that the chronic low-level environmental lead exposure may interfere with urate excretion of CRI patients. Importantly, the inhibition of urate excretion can be markedly improved by lead chelating therapies. These data shed light on additional treatment of CRI patients with gout; however, more studies are needed to confirm our findings.

Adult↗
PubMed2001

Mycophenolate mofetil reduces renal cortical inducible nitric oxide synthase mRNA expression and diminishes glomerulosclerosis in MRL/lpr mice.

Overexpression of inducible nitric oxide synthase (iNOS) has been implicated in the pathogenesis of lupus glomerulonephritis. Mycophenolate mofetil (MMF), a novel immunosuppressive agent, is currently used in organ transplantation and under evaluation for treatment of autoimmune disorders. Mycophenolic acid, the active metabolite of MMF, has been shown to suppress cytokine-induced nitric oxide production in vitro. The aim of this study was to evaluate the effect of MMF on the expression of renal cortical iNOS mRNA and protection against glomerulonephritis in MRL/lpr mice. Three-month-old MRL/lpr mice (n = 6) displaying clinical symptoms of glomerulonephritis were treated for 3 months with MMF (90 mg/kg/day) dissolved in a vehicle. Controls were age- and sex-matched mice (n = 6) that received the vehicle alone. By reverse-transcription competitive polymerase chain reaction, we found that the renal cortical iNOS/beta-actin mRNA ratio was reduced by 30.8% (P <.05) in MMF-treated mice. Furthermore, MMF significantly reduced urinary nitrite production and degree of glomerulosclerosis. The glomerular volume was reduced by 17.5% (P <.001). Proteinuria was also significantly reduced in the MMF-treated group. However, by electrophoretic mobility shift assay, the nuclear binding of nuclear factor-kappaB (NF-kappaB) was not affected by MMF treatment. We conclude that in addition to its immunosuppressive action, MMF may reduce renal cortical iNOS mRNA expression and diminish glomerulosclerosis in MRL/lpr mice independent of modulation of the NF-kappaB pathway.

Animals↗
PubMed2001

Oxygen- and growth rate-dependent regulation of Escherichia coli fumarase (FumA, FumB, and FumC) activity.

Escherichia coli contains three biochemically distinct fumarases which catalyze the interconversion of fumarate to L-malate in the tricarboxylic acid cycle. Batch culture studies indicated that fumarase activities varied according to carbon substrate and cell doubling time. Growth rate control of fumarase activities in the wild type and mutants was demonstrated in continuous culture; FumA and FumC activities were induced four- to fivefold when the cell growth rate (k) was lowered from 1.2/h to 0.24/h at 1 and 21% O(2), respectively. There was a twofold induction of FumA and FumC activities when acetate was utilized instead of glucose as the sole carbon source. However, these fumarase activities were still shown to be under growth rate control. Thus, the activity of the fumarases is regulated by the cell growth rate and carbon source utilization independently. Further examination of FumA and FumC activities in a cya mutant suggested that growth rate control of FumA and FumC activities is cyclic AMP dependent. Although the total fumarase activity increased under aerobic conditions, the individual fumarase activities varied under different oxygen levels. While FumB activity was maximal during anaerobic growth (k = 0.6/h), FumA was the major enzyme under anaerobic cell growth, and the maximum activity was achieved when oxygen was elevated to 1 to 2%. Further increase in the oxygen level caused inactivation of FumA and FumB activities by the high oxidized state, but FumC activity increased simultaneously when the oxygen level was higher than 4%. The same regulation of the activities of fumarases in response to different oxygen levels was also found in mutants. Therefore, synthesis of the three fumarase enzymes is controlled in a hierarchical fashion depending on the environmental oxygen that the cell encounters.

Cell Division↗
PubMed2001

In vivo pressure-flow curve in unilateral rat lung ischemia-reperfusion injury.

The pressure-flow (P-Q) curve has been widely used in many studies to describe the effects of various factors on vascular hemodynamics. It is not clear, however, whether unilateral ischemia-reperfusion (IR) alters the P-Q curve of the rat lung. In this study, we developed an in vivo P-Q curve using the unilateral (left) rat lung before and after IR. Animals were divided into two groups: sham and IR. The protocol of the IR group consisted of three periods: baseline, ischemia, and reperfusion. P-Q curves were obtained by altering blood flow of the left lung during the baseline and the reperfusion periods. The sham group received the same operation without IR procedure. An additional group was used to compare pulmonary blood flow measured by the microsphere and the ultrasonic methods. IR treatment rotated the P-Q curve toward the left, indicating an increase in resistance in the left lung. However, this rotation was not found in the sham group. A significant correlation (r = 0.87, P < 0.01) between percentages of blood flow obtained by the microsphere and ultrasonic methods in both right and left lungs was demonstrated. Therefore, we demonstrated a simple and useful technique to evaluate changes in the P-Q curves caused by IR in the unilateral rat lung model.

Animals↗
PubMed2001

Dual effect of the antianginal drug fendiline on bladder female transitional carcinoma cells: mobilization of intracellular CA2+ and induction of cell death.

The effect of fendiline, an antianginal drug, on cytosolic free Ca2+ levels ([Ca2+]i) in populations of bladder female transitional carcinoma (BFTC) cells was explored using fura-2 as a Ca2+ indicator. Fendiline at concentrations between 3 and 200 micromol/l increased [Ca2+]i in a concentration-dependent manner and the signal saturated at 100 micromol/l. The [Ca2+]i signal was biphasic, with an initial rise and a slow decay. Ca2+ removal inhibited the Ca2+ signal by about half in peak amplitude. Adding 3 mmol/l Ca2+ increased [Ca2+]i in cells pretreated with 100 micromol/l fendiline in Ca2+ -free medium, suggesting that fendiline induced Ca2+ influx via capacitative Ca2+ entry. In Ca2+ -free medium, pretreatment with 1 micromol/l thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor) to deplete the endoplasmic reticulum Ca2+ store inhibited most of the 100 micromol/l fendiline-induced internal Ca2+ release; and conversely, pretreatment with 100 micromol/l fendiline partly inhibited 1 micromol/l thapsigargin-induced Ca2+ release. This indicates that the major internal Ca2+ store of fendiline-induced [Ca2+]i increases is located in the endoplasmic reticulum. The Ca2+ release induced by 100 micromol/l fendiline may be partly mediated by inositol 1,4,5-trisphosphate, because the [Ca2+]i increase was inhibited by 50% by inhibiting phospholipase C with 2 micromol/l U73122. Fendiline (100 micromol/l) decreased cell viability by 12-44% after being added to cells for 2- 30 min. Together, the findings indicate that in BFTC cells, fendiline exerts a dual effect: mobilization of intracellular Ca2+ and induction of cell death.

Anti-Arrhythmia Agents↗
PubMed2001

Comparison of speech results after Furlow palatoplasty and von Langenbeck palatoplasty in incomplete cleft of the secondary palate.

BACKGROUND: Due to many confounding factors, it is not easy to answer which method of cleft repair is superior to others. The purpose of this study is to try to compare the treatment result of different types of palatoplasty in patients who had the same cleft type and same treatment protocol besides the method of cleft repair. We selected nonsyndromic patients with incomplete cleft of the secondary palate. The speech results after the two palatoplasties were compared. METHODS: Ninety-six children with nonsyndromic incomplete clefts of the secondary palate who received palatoplasty at the Craniofacial Center of Chang Gung Memorial Hospital from 1989 to 1997 were studied. Forty-six patients received Furlow palatoplasty and 50 patients received von Langenbeck palatoplasty. Velopharyngeal function was evaluated by speech pathologists periodically after the patient was two and half years old. Adequacy of velopharyngeal function was used as a measurement of speech outcome. RESULTS: The Furlow palatoplasty group showed excellent results with 98% (45/46) adequacy in velopharyngeal function. In the von Langenbeck palatoplasty group, only 70% (35/50) of the patients had adequate velopharyngeal function. Statistical analysis with Fisher's exact test showed a significant difference (p < 0.0001, p < 0.05). Only one patient had an oronasal fistula after Furlow palatoplasty. After von Langenbeck palatoplasty, one patient had an oronasal fistula and one had wound dehiscence. CONCLUSION: In this study, there was a better speech outcome after Furlow palatoplasty than von Langenbeck palatoplasty for repair of incomplete cleft of the secondary palate. Also, the number of complications after a Furlow palatoplasty was low. It should be a recommended treatment.

Cleft Palate↗
PubMed2000

NPC-15199, a novel anti-inflammatory agent, mobilizes intracellular Ca2+ in bladder female transitional carcinoma (BFTC) cells.

This report demonstrates that NPC-15199 [(N-(9-fluorenylmethoxycarbonyl)L-leucine)], a novel anti-inflammatory agent, increases intracellular Ca2+ concentration ([Ca2+]i) in human bladder female transitional cancer (BFTC) cells. Using fura-2 as a Ca2+ probe, NPC-15199 (0.1-2 mM) was found to increase [Ca2+]i concentration-dependently. The response saturated at 2-5 mM NPC-15199. The [Ca2+]i increase comprised an initial rise, a slow decay, and a plateau. Ca2+ removal partly inhibited the Ca2+ signals. In Ca2+-free medium, pretreatment with 1 mM NPC-15199 abolished the [Ca2+]i increase induced by 1 microM thapsigargin (an endoplasmic reticulum Ca2+ pump inhibitor); and after pretreatment with thapsigargin, NPC-15199-induced Ca2+ release was dramatically inhibited. This indicates that NPC-15199 released internal Ca2+ mostly from the endoplasmic reticulum. Adding 3 mM Ca2+ increased [Ca2+]i in cells pretreated with 1 mM NPC-15199 in Ca2+-free medium. Together, the findings suggest that in BFTC bladder cancer cells, NPC-15199 induced Ca2+ release from the endoplasmic reticulum and activating Ca2+ entry.

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed2000

Ectopic pancreatic rests: a rare cause of persistent umbilical discharge.

Ectopic pancreatic rests are rare. We report two cases discovered in infants who underwent surgical exploration of the umbilicus for persistent umbilical discharge with peri-umbilical excoriation. A shallow sinus leading to a firm cyst was excised in both infants, and histopathological study confirmed the presence of exocrine and endocrine pancreatic tissue. There is only one other case of ectopic umbilical pancreatic tissue reported, and this was in a patient presenting with an umbilical mass.

Choristoma↗
PubMed2000

Clomiphene, an ovulation-inducing agent, mobilizes intracellular Ca2+ and causes extracellular Ca2+ influx in bladder female transitional carcinoma cells.

BACKGROUND/METHODS: The effect of clomiphene, an ovulation-inducing agent, on cytosolic free Ca2+ levels ([Ca2+]i) in populations of BFTC human bladder cancer cells was explored by using fura-2 as a Ca2+ indicator. RESULTS: Clomiphene at concentrations between 10 and 75 microM increased [Ca2+]i in a concentration-dependent manner and the signal saturated at 50 microM. The [Ca2+]i signal was biphasic with an initial rise and a slow decay. Ca2+ removal inhibited the Ca2+ signal by about 40-50% in maximum [Ca2+]i. Adding 3 mM Ca2+ increased [Ca2+]i in cells pretreated with 50 microM clomiphene in Ca2+-free medium, suggesting that clomiphene induced capacitative Ca2+ entry. In Ca2+-free medium, pretreatment with 50 microM brefeldin A (to disrupt the Golgi complex Ca2+ store), 1 microM thapsigargin (to inhibit the endoplasmic reticulum Ca2+ pump), and CCCP (to uncouple mitochondria) inhibited 85% of clomiphene-induced intracellular Ca2+ release. Conversely, pretreatment with 50 microM clomiphene in Ca2+-free medium abolished the [Ca2+]i increase induced by brefeldin, thapsigargin or CCCP. The intracellular Ca2+ release was unaltered by inhibiting formation of inositol-1,4,5-trisphosphate (IP3) with 2 mM 1-(6-((17beta-3-methoxyestra-1,3,5(10)-trien-17-yl)amino)hexyl)-1H-pyrrole-2,5-dione (U73122; a phospholipase C inhibitor). CONCLUSION: The [Ca2+]i increase induced by 50 microM clomiphene was not affected by 10 microM of nifedipine, verapamil or diltiazem. Collectively, the results suggest that clomiphene releases intracellular Ca2+ in an IP3-independent manner and also activates extracellular Ca2+ influx.

Calcium↗
PubMed1999

Novel strategy for efficient screening and construction of host/vector systems to overproduce penicillin acylase in Escherichia coli.

A novel and simple method of using penicillin for screening of mutant strains with a high penicillin acylase (PAC) activity was developed. Random mutagenesis was conducted using a PAC-producing strain resistant to 6-aminopenicillanic acid (6-APA) as the parent strain and mutants were screened with penicillin at a high concentration. Results suggest that mutants with a high minimum inhibitory concentration for penicillin (MIC(penG)) usually overproduce PAC. Both volumetric and specific PAC activities of a mutant, MD7, were significantly higher than those of the parent strain, HBPAC101 harboring pCLL2902. The mutation(s) resulting in the enhanced expression was mapped on the host chromosome rather than the plasmid. In addition, the mutant strain of MDDeltaP7, derived by elimination of the harbored plasmid in MD7, was demonstrated to be efficient in production of PAC by using the expression plasmids for which expression of the pac gene is limited by translation. An extremely high specific PAC activity of more than 350 U/L/OD(600) was reached upon cultivation of MDDeltaP7 harboring pTrcKnPAC2902 in a bioreactor. As such, the strategy is effective in terms of constructing PAC overproducers and improving the process yield for production of PAC.

Bioreactors↗
PubMed1999

The role of components of recombination signal sequences in immunoglobulin gene segment usage: a V81x model.

It has long been appreciated that some immunoglobulin (and T-cell receptor) gene segments are used much more frequently than others. The VHsegment V81x is a particularly striking case of overusage. Its usage varies with the stage of B-cell development and with the strain of mice, but it is always high in B cell progenitors. We have found that the coding sequence and the recombination signal sequences (RSS) are identical in five mouse strains, including CAST/Ei, a strain derived from the species Mus castaneus. Thus, the strain differences cannot be attributed to sequences within V81x itself. V81x RSS mediated recombination at rates significantly higher than another VHRSS. Although the V81x nonamer differs at one base pair from the consensus sequence, an RSS with this nonamer and a consensus heptamer recombines as well as the consensus RSS. When the V81x spacer is replaced by that of VA1, the frequency of recombination decreases by approximately 5-fold; thus, the contribution of variation in natural spacers to variability in VHusage in vivo is likely to be more than has been previously appreciated. Furthermore, the contribution of the heptamer and nonamer to differential VHusage in our assay is correlated inversely with their conservation throughout the VHlocus.

Animals↗