Condom use among women choosing long-term hormonal contraception

CONTEXT

Women who rely on long-term hormonal contraception may neglect to use condoms, and thus increase their risk of contracting sexually transmitted diseases, including AIDS.

METHODS

Data from a prospective, multisite study were collected to examine the probability of condom use among 1,073 new users of either the contraceptive implant or injectable; users were interviewed when they accepted their method and again six months to one year later. Multivariate logistic regression analyses identified factors that significantly predicted the likelihood of dual method use.

RESULTS

Condom use dropped markedly among women who adopted long-term hormonal contraception. The proportion who always used condoms in the previous three months fell from 21% at the time of adoption to 11% at follow-up. Among women with one sexual partner, this decrease was from 20% to 10%; however, among those with more than one partner, use increased from 25% to 31%. The factors significantly predicting dual method use included previous condom use (odds ratio of 2.5), receipt of AIDS-specific counseling (odds ratio of 1.6), the perception of being at some risk of AIDS at baseline (odds ratio of 1.4) and having had more than one sexual partner over the study period (odds ratio of 5.4). In addition, injectable users, teenagers and black women were more likely than other women to use condoms with their hormonal method.

CONCLUSIONS

Although condom use among all women declined markedly once they initiated long-term hormonal contraception, frequency of condom use varied by subgroup and was associated with several factors. Most importantly, women with more than one sexual partner and those who received a message during counseling on the need to continue using condoms were more likely than others to use condoms in conjunction with the implant or injectable.

Anaesthetic management of the surgical separation of a pair of thoracopagus-cardiopagus twins

We describe the anaesthetic management of the surgical separation of a pair of thoracopagus-cardiopagus twins with a common right atrium and a myocardial tissue bridge containing vascular channels between their ventricles. One of them died during the procedure, the surviving twin is now two years old. The survival of one twin for two years without significant sequelae, after the surgical separation of twins with shared right atrium and fused ventricles, has not previously been reported. Careful preoperative assessment is essential to anticipate potential serious problems during the procedure.

Genes essential for nod factor production and nodulation are located on a symbiotic amplicon (AMPRtrCFN299pc60) in Rhizobium tropici

Amplifiable DNA regions (amplicons) have been identified in the genome of Rhizobium etli. Here we report the isolation and molecular characterization of a symbiotic amplicon of Rhizobium tropici. To search for symbiotic amplicons, a cartridge containing a kanamycin resistance marker that responds to gene dosage and conditional origins of replication and transfer was inserted in the nodulation region of the symbiotic plasmid (pSym) of R. tropici CFN299. Derivatives harboring amplifications were selected by increasing the concentration of kanamycin in the cell culture. The amplified DNA region was mobilized into Escherichia coli and then into Agrobacterium tumefaciens. The 60-kb symbiotic amplicon, which we termed AMPRtrCFN299pc60, contains several nodulation and nitrogen fixation genes and is flanked by a novel insertion sequence ISRtr1. Amplification of AMPRtrCFN299pc60 through homologous recombination between ISRtr1 repeats increased the amount of Nod factors. Strikingly, the conjugal transfer of the amplicon into a plasmidless A. tumefaciens strain confers on the transconjugant the ability to produce R. tropici Nod factors and to nodulate Phaseolus vulgaris, indicating that R. tropici genes essential for the nodulation process are confined to an ampliable DNA region of the pSym.

Multiple recombination events maintain sequence identity among members of the nitrogenase multigene family in Rhizobium etli

A distinctive characteristic of the Rhizobium genome is the frequent finding of reiterated sequences, which often constitute multigene families. Interestingly, these families usually maintain a high degree of nucleotide sequence identity. It is commonly assumed that apparent gene conversion between reiterated elements might lead to concerted variation among members of a multigene family. However, the operation of this mechanism has not yet been demonstrated in the Rhizobiaceae. In this work, we employed different genetic constructions to address the role of apparent gene conversion as a homogenizing mechanism between members of the plasmid-located nitrogenase multigene family in Rhizobium etli. Our results show that a 28-bp insertion into one of the nitrogenase reiterations can be corrected by multiple recombination events, including apparent gene conversion. The correction process was dependent on the presence of both a wild-type recA gene and wild-type copies of the nitrogenase reiterations. Frequencies of apparent gene conversion to the wild-type nitrogenase reiterations were the same when the insertion to be corrected was located either in cis or in trans, indicating that this event frequently occurs through intermolecular interactions. Interestingly, a high frequency of multiple crossovers was observed, suggesting that these large plasmid molecules are engaging repeatedly in recombination events, in a situation akin to phage recombination or recombination among small, high-copy number plasmids.

Candidate genes in complete and partial XY sex reversal: mutation analysis of SRY, SRY-related genes and FTZ-F1

The sexual phenotype is established in three steps: (1) the sex chromosome constitution; (2) the differentiation of the gonads; and (3) the response of the internal and external genitalia to the hormones produced by the differentiated gonads. Errors that occur at any of these stages can result in defective sexual differentiation. Therefore the investigation of patients with abnormalities of testis development will help elucidate the mechanisms of sex determination and gonadal differentiation. It was in this way that SRY. the primary testis determining gene was identified. De novo mutations in SRY, result in gonadal dysgenesis by disrupting the DNA-binding activity of the SRY protein. However, only 20% of cases of gonadal dysgenesis, are explained by mutations in SRY or its flanking sequences. Therefore, there are several pieces to this puzzle yet to be discovered and it is hoped that mutation analysis of other genes implicated in gonadal development and differentiation may shed some light on aetiology of gonadal dysgenesis in the remaining 80% of cases.

Gene amplification and genomic plasticity in prokaryotes

Gene amplification is a common feature of the genome of prokaryotic organisms. In this review, we analyze different instances of gene amplification in a variety of prokaryotes, including their mechanisms of generation and biological role. Growing evidence supports the concept that gene amplification be considered not as a mutation but rather as a dynamic genomic state related to the adaptation of bacterial populations to changing environmental conditions or biological interactions. In this context, the potentially amplifiable DNA regions impose a defined dynamic structure on the genome. If such structure has indeed been selected during evolution, it is a particularly challenging hypothesis.

Description of the characteristics of cases with noncontiguous neural tube defects identified in a series of consecutive births

Van Allen et al. [(1973) Am. J. Med. Genet. 47:723-743] provided evidence for multisite closure of the neural tube in humans. Reynolds et al. [(1995) Proceedings of the Greewood Genetic Center 14:70-71] and Seller [(1995) J. Med. Genet. 32:205-207] described 13 and seven cases of noncontiguous neural tube defects (NTDs) respectively and concluded that the presence of noncontiguous NTDs cannot be explained on the basis of the model of a single initiation site with bidirectional closure. Here we present a series of 14 consecutive infants with noncontiguous NTDs, describing their characteristics. These show that noncontiguous NTDs are clinically heterogeneous, may have differences in sex ratio, and could have causal heterogeneity. The different combinations of closure failure defects have shown proportions in our population that are different from those in the populations studied by Reynolds et al. and Seller.

Injectable contraceptive discontinuation and subsequent unintended pregnancy among low-income women

OBJECTIVES

This study investigated rates of discontinuation of the recently introduced injectable contraceptive depot medroxyprogesterone acetate (DMPA) and postdiscontinuation rates of unprotected intercourse and unintended pregnancy.

METHODS

A sample of 402 low-income, urban, minority women were interviewed when they initiated DMPA use and 12 months later.

RESULTS

The 12-month life-table discontinuation rate was 58%, with half of the discontinuers stopping after only one injection. Menstrual changes and other side effects were the most frequently cited reasons for discontinuation. Approximately half of the discontinuers at risk for unintended pregnancy either did not make the transition to another contraceptive or used contraception only sporadically. The cumulative unintended pregnancy rate by 9 months postdiscontinuation was 20%.

CONCLUSIONS

DMPA initiators were at substantial risk for unintended pregnancy because most quickly discontinued use and did not make the transition to consistent use of another contraceptive.

[Internal ophthalmoplegia: a rare complication of varicella]

INTRODUCTION

Internal ophthalmoplegia complicating Chickenpox is rare. Fifteen cases have been reported so far.

CLINICAL CASE

We reported a new case of this neurological complication in a 3 1/2 year old girl that 6 days after the onset of the typical rash, the right pupil was dilated and fixed to light and accommodation. Pupillary dilatation and accommodative paralysis persist after five years, but spectacle correction has restored the visual acuity.

Generation of Rhizobium strains with improved symbiotic properties by random DNA amplification (RDA)

To select for bacterial strains with enhanced phenotypes, random fragments of a whole genome, or a defined region of the genome, are cloned in a nonreplicating vector. The resulting plasmids are integrated by recombination into the homologous DNA region of the original strain. Integration gives rise to a nontandem direct duplication of the corresponding DNA region separated by the vector moiety of the plasmid. Recombination between the direct repeats leads to tandem duplication and further amplification of the entire integrated DNA, including the vector. Bacteria harboring the amplified DNA are selected by increasing the dosage of an antibiotic corresponding to a resistance marker of the integrated vector. Pooled strains carrying amplifications are then challenged with a selective pressure for the desired phenotype. After repeated selection cycles, the most fit strains are isolated. We used this process, which we called random DNA amplification, to select Rhizobium strains with increased competitiveness for nodule formation. Derivatives containing randomly amplified DNA regions of the symbiotic plasmid of Rhizobium tropici CFN299 strain were generated. Pools of amplified strains were inoculated onto various tropical legumes. After several cycles of selection through plants, amplified derivatives showing an increased competitiveness for nodule formation with the leguminous plant Macroptilium atropurpureum were obtained.

[A new classification of lower infarcts with important prognostic significance]

BACKGROUND

The initial therapy of acute myocardial infarction is often determined by the electrocardiogram.

OBJECTIVE

To evaluate a classification of inferior myocardial infarctions according to the first electrocardiogram.

DESIGN AND SETTING

Prospective study in a coronary care unit.

PATIENTS

116 patients admitted due to a first acute myocardial infarction of the inferior wall.

METHODS

"Type 1" electrocardiogram was defined as ST segment elevation without distortion of the QRS. Patients were considered "type 2" when, besides ST segment elevation, they presented a distortion of the terminal portion of the QRS complex in two inferior leads.

MAIN RESULTS

Twenty-nine patients (25%) were considered "type 2". These patients were older and had worse Killip class than "type 1". The mortality rate was 1.2% in "type 1", and 24.1% in "type 2" (p = 0.0002). After multivariate analysis, which included Killip class, age, smoking, type of electrocardiogram and fibrinolysis, the type of electrocardiogram remained significantly predictive of death (p = 0.014).

CONCLUSIONS

We conclude that "type 2" electrocardiogram is an independent predictor of adverse outcome in inferior infarctions. Further investigation is needed concerning its implications in the clinical management of these patients, although reperfusion therapy is warranted.

Inflammatory extracavitary right atrial mass and pulmonary thromboembolism

A 40 year old male patient diagnosed as having pulmonary thromboembolism, was found to have a right atrial mass, after being subjected to an echocardiogram, a CT thoracic Scan and magnetic resonance imaging. An intracardiac exploration by cardiopul-monary bypass was performed. The mass was located and excised, but in fact found to be an extracardiac, inflammatory and cavitated mass. The wall of the right atrium was infiltrated due to the inflammatory process. This case illustrates the advantage of echocardiography, followed by surgery, in the clinical diagnosis and also shows how to treat cardiac masses and tumors.

Sinus tachycardia and J wave masquerading as atrial flutter

The admission electrocardiogram (ECG) from a patient with severe heart failure was considered diagnostic of atrial flutter with 2:1 atrioventricular conduction. Slowing of the heart rate revealed sinus tachycardia with prominent 'J' waves that had been previously thought to be 'F' waves.

Discrete amplifiable regions (amplicons) in the symbiotic plasmid of Rhizobium etli CFN42

Frequent tandem amplification of defined regions of the genome, called amplicons, is a common characteristic in the genomes of some Rhizobium species, such as Rhizobium etli. In order to map these zones in a model Rhizobium replicon, we undertook an analysis of the plasticity patterns fostered by amplicons in the pSym (390 kb) of R. etli CFN42. Data presented in this article indicate the presence of four amplicons in pSym, used for the generation of tandem amplifications and deletions. The amplicons are large, ranging from 90 to 175 kb, and they are overlapping. Each amplicon is usually flanked by specific reiterated sequences. Formation of amplifications and deletions requires an active recA gene. All the amplicons detected are concentrated in a zone of roughly one-third of pSym, covering most of the symbiotic genes detected in this plasmid. No amplicons were detected in the remaining two-thirds of pSym. These data support the idea that most of the known symbiotic genes in this plasmid are located in a genomic region that is prone to the formation of frequent tandem amplification.

[Age is the independent prognostic factor in acute myocardial infarct. The clinical course of infarct in the elderly patient]

We analyze the influence of age in the evolution of patients with acute myocardial infarction admitted to our Coronary Care Unit throughout two years (1990 and 1991). All 542 patients admitted during this period were classified in three groups: 299 less than 65 year old (group A), 170 between 65 and 74 year old (group B), and 73 with 75 year old or more (group C). Aged patients had a worse clinical condition, with significantly more previous heart failure, diabetes or hypertension, and the Killip's class was worse in group C than in group B, and worse in this than in group A (p = 0.00000). The mortality rate was 6.7% in group A, 12.9% in group B, and 31.5% group C (p = 0.00000). After a multivariate analysis, only three factors were significantly associated to prognosis: previous stroke, Killip's class, and group of age. Fibrinolytic therapy and coronary arteriography were less frequent with old people (p = 0.00000 and p = 0.00000 respectively). We conclude that age is an independent factor of prognosis during myocardial infarction. Old people have a worse clinical condition and the treatment is less aggressive than in young people.

Acute myocardial infarction in a young man after heat exhaustion

A 33-year-old man with heat exhaustion was admitted to our hospital suffering from severe chest pain. Serum creatine kinase elevation and new Q waves revealed myocardial infarction of the inferior wall. Technetium-99m-pyrophosphate suggested diffuse myocardial damage, although the left ventricular function was normal by echocardiography. This case highlights the importance of early recognition of heat stroke and heat exhaustion, as they are associated with widespread tissue injury.

[Tuberculous splenic abscess in an immunocompetent patient]

Splenic tuberculosis is a rare entity. The case of an 18-year old patient admitted for fever and general malice is described. Echography and abdominal CT showed a hypodense image localized in the spleen. Splenic tuberculosis was diagnosed upon observation of alcohol acid resistant bacilli (AARB) in the biopsy obtained by punction of the abscess. Correct tuberculostatic treatment led to disappearance of the splenic abscess with no further therapeutic measures being required.

Transient myocardial injury after elective electrical cardioversion

A patient with recent myocardial infarction underwent elective direct current countershock because of atrial fibrillation. After several shocks, the ST segments were strikingly raised throughout the precordial leads, which disappeared with the administration of a perfusion of nitroglycerin. This case is evidence that electrical cardioversion can cause myocardial damage.

Anorexia nervosa and myocardial infarction

A 39-year-old woman with long-standing anorexia nervosa was admitted to our hospital because of extreme weakness and cachexia. During a hyperalimentation therapy, she developed chest pain, revealing the electrocardiogram and cardiac enzymes a myocardial infarction of the inferior wall. We suggest that anorexia nervosa does not 'protect' against coronary atherosclerosis, and that some of the cases of sudden death could be related to myocardial ischemia.

Short rib-polydactyly syndrome and pericentric inversion of chromosome 4

We report on a newborn infant with clinical and radiological manifestations of some type of short rib-polydactyly syndrome who died soon after birth. Chromosomal studies on peripheral blood lymphocytes and chondrocytes demonstrated an apparently balanced pericentric inversion of chromosome 4 (present in the mother also). This association may have occurred by chance but, if not, the chromosomal breakpoints could interrupt the gene responsible for short rib-polydactyly syndromes, or else be related to the mechanism of short rib-polydactyly syndromes.

Resistance to the cereal cyst nematode (Heterodera avenae Woll.) transferred from the wild grassAegilops ventricosa to hexaploid wheat by a "stepping-stone" procedure

Transfer of resistance toHeterodera avenae, the cereal cyst nematode (CCN), by a "stepping-stone" procedure from the wild grassAegilops ventricosa to hexaploid wheat has been demonstrated. The number of nematodes per plant was lower, and reached a plateau much earlier, in the resistant introgression line H93-8 (1-2 nematodes per plant) than in the recipient H10-15 wheat (14-16 nematodes per plant). Necrosis (hypersensitive reaction) near the nematode, little cell fusion, and few, often degraded syncytia were observed in infested H93-8 roots, while abundant, well-formed syncytia were present in the susceptible H10-15 wheat. Line H93-8 was highly resistant to the two Spanish populations tested, as well as the four French races (Fr1-Fr4), and the British pathotype Hall, but was susceptible to the Swedish pathotypes HgI and HgIII. Resistance was inherited as though determined by a single quasi-dominant factor in the F2 generations resulting from crosses of H93-8 with H10-15 and with Loros, a resistant wheat carrying the geneCre1 (syn.Ccn1). The resistance gene in H93-8 (Cre2 orCcn2) is not allelic with respect to that in Loros. RFLPs and other markers, together with the cytogenetical evidence, indicate that theCre2 gene has been integrated into a wheat chromosome without affecting its meiotic pairing ability. Introduction ofCre2 by backcrossing into a commercial wheat backgroud increases grain yield when under challenge by the nematode and is not detrimental in the absence of infestation.

Syncope and long QT syndrome with an initially normal QT interval

We present two patients who were admitted to our Hospital because of repetitive syncopal attacks. The study previous to their admission included electrocardiograms in which the QT interval was normal. During their admission, an striking lengthening of the QT interval, in addition to other criteria of the long QT syndrome, was observed in both patients. We suggest that one normal measurement of the QT interval should not rule out this diagnosis.

Gene amplification in Rhizobium: identification and in vivo cloning of discrete amplifiable DNA regions (amplicons) from Rhizobium leguminosarum biovar phaseoli

A genetic element that allows the positive selection of different genomic rearrangements was used to analyze DNA amplification in Rhizobium leguminosarum biovar phaseoli. Discrete amplifiable DNA regions (amplicons) were detected in different regions of the genome of the model strain CFN42, including the chromosome and several large plasmids. Amplicons were mobilized into Escherichia coli using a genetic approach that involves the introduction of an origin of replication active in E. coli and an origin of conjugal transfer into the amplifiable DNA regions of the Rhizobium genome. The strategy can be a valuable tool for studies on genome organization and function. We propose that amplicons define a structural characteristic of the genome that may play an important biological role.

Copy number and location of insertion sequences ISS1 and IS981 in lactococci and several other lactic acid bacteria

Genomic DNA from 49 lactococcal strains was screened by Southern hybridization for the presence and relative copy number of lactococcal insertion sequence ISS1: ISS1 was found in 47 of 49 strains giving 1 to 20 hybridizing bands per strain. Southern hybridizations of undigested plasmid DNA from 17 lactococcal strains probed with ISS1 and IS981 showed that ISS1 was present on plasmids in all 17 strains, whereas IS981 was present on plasmids in 14 of the 17 strains. Both insertion sequences were present primarily on larger plasmids (> 25 kb), and some plasmids contained copies of both insertion sequences. When probed with ISS1, Southern hybridizations of DNA isolated from Lactococcus lactis ssp. lactis ML3 frozen stock culture and from isolated colonies showed that the stock culture consisted of a mixture of cells having different ISS1-hybridizing bands, indicating that stock cultures may contain cells with varying locations of ISS1 sequences. The number of copies and their widespread distribution among lactococcal strains establish that insertion sequences will contribute significantly to genotypic and phenotypic events that may affect the industrial performance and stability of lactococcal strains.

Different plasmids of Rhizobium leguminosarum bv. phaseoli are required for optimal symbiotic performance

Rhizobium leguminosarum bv. phaseoli CFN42 contains six plasmids (pa to pf), and pd has been shown to be the symbiotic plasmid. To determine the participation of the other plasmids in cellular functions, we used a positive selection scheme to isolate derivatives cured of each plasmid. These were obtained for all except one (pe), of which only deleted derivatives were recovered. In regard to symbiosis, we found that in addition to pd, pb is also indispensable for nodulation, partly owing to the presence of genes involved in lipopolysaccharide synthesis. The positive contribution of pb, pc, pe, and pf to the symbiotic capacity of the strain was revealed in competition experiments. The strains that were cured (or deleted for pe) were significantly less competitive than the wild type. Analysis of the growth capacity of the cured strains showed the participation of the plasmids in free-living conditions: the pf- strain was unable to grow on minimal medium, while strains cured of any other plasmid had significantly reduced growth capacity in this medium. Even on rich medium, strains lacking pb or pc or deleted for pe had a diminished growth rate compared with the wild type. Complementation of the cured strains with the corresponding wild-type plasmid restored their original phenotypes, thus confirming that the effects seen were due only to loss of plasmids. The results indicate global participation of the Rhizobium genome in symbiotic and free-living functions.

The multiple-minima problem in small peptides revisited. The Threshold Accepting approach

A recently reported optimization method, known as Threshold Accepting, was tested for the purpose of locating the structure of several peptide molecules with the lowest conformational energy. A comparison with previous results obtained with the Simulated Annealing technique was made. Our study indicate Threshold Accepting as a better technique in locating such structures.

Prevention of Myocardial Infarction by Nitroglycerin plus Intravenous Beta-Blockers

Seven patients with ongoing angina with ST-segment elevation, refractory to oral nifedipine and intravenous nitroglycerin, were treated by adding intravenous beta-blockers. Chest pain resolved in all of them in a few minutes, and myocardial infarction did not develop in 5 patients. We recommend this approach for patients to whom thrombolytics are contraindicated or have been very recently administered, although further investigation is needed to extend its application more widely. It does not preclude the use of other therapies, if considered necessary.

Molecular cloning and characterization of the recA gene of Rhizobium phaseoli and construction of recA mutants

The Rhizobium phaseoli recA gene has been cloned by interspecific complementation of the Fec phenotype of bacteriophage lambda. The cloned gene restored the recombination proficiency and conferred resistance to DNA-damaging agents (methyl methanesulfonate and nitrofurantoin) to an Escherichia coli recA mutant. The direction of transcription and the localization of the recA gene were determined by mutagenesis with phage MudIIPR13 and heterologous hybridization with an E. coli recA probe. An R. phaseoli recA::Spcr mutation was introduced in two R. phaseoli strains by homogenotization. The R. phaseoli recA mutants were more sensitive to DNA-damaging agents and exhibited a 100-fold reduction in recombination frequency as compared with their parental strains. A deletion of the symbiotic plasmid abolishing nodulation was found at high frequency (10(-2)) in R. phaseoli CNF42. This event was recA dependent. In R. phaseoli CFN285, two events of symbiotic instability were found at high frequency (10(-3]: one was a deletion in the symbiotic plasmid, and the other was the loss of whole symbiotic plasmid. In the CFN285 recA::Spcr mutant, only the loss of the symbiotic plasmid was observed.

Structural complexity of the symbiotic plasmid of Rhizobium leguminosarum bv. phaseoli

The complete physical map of the symbiotic plasmid of Rhizobium leguminosarum bv. phaseoli strain CFN42 was established. The data support the concept that Rhizobium symbiotic genes are part of a complex genomic structure which contains a large amount of reiterated DNA sequences. This plasmid is a circular structure of 390 kb with approximately 10 families of internally reiterated DNA sequences of two to three elements each. One family includes two directly oriented nitrogenase operons situated 120 kb apart. We also found several stretches of pSym that are reiterated in other replicons of the cell. Localization of symbiotic gene sequences by heterologous hybridization revealed that nodABC sequences are separated in two regions, each of which contains a nod boxlike element, and it also suggested the presence of two copies of the nifA and nodD gene sequences. We propose that the complex structure of the symbiotic plasmid allows interactions between repeated DNA sequences which, in turn, might result in frequent rearrangements.

Amplification and deletion of a nod-nif region in the symbiotic plasmid of Rhizobium phaseoli

One remarkable characteristic of the genomes of some Rhizobium species is the frequent occurrence of rearrangements. In some instances these rearrangements alter the symbiotic properties of the strains. However, no detailed molecular mechanisms have been proposed for the generation of these rearrangements. To understand the mechanisms involved in the formation of rearrangements in the genome of Rhizobium phaseoli, we have designed a system which allows the positive selection for amplification and deletion events. We have applied this system to investigate the stability of the symbiotic plasmid of R. phaseoli. High-frequency amplification events were detected which increase the copy number of a 120-kb region carrying nodulation and nitrogen fixation genes two to eight times. Deletion events that affect the same region were also found, albeit at a lower frequency. Both kinds of rearrangements are generated by recombination between reiterated nitrogenase (nifHDK) operons flanking the 120-kb region.

Applications of simulated annealing to the multiple-minima problem in small peptides

A Simulated Annealing method has been implemented to overcome the multiple minima problem inherent in finding the global minimum of small peptides with 2, 3, 5, 10 and 24 dihedral angles. The algorithm works much better if one introduces the anticorrelations observed in Molecular Dynamics.

Genomic instability in Rhizobium phaseoli

Experience from different laboratories indicates that Rhizobium strains can generate variability in regard to some phenotypic characteristics such as colony morphology or symbiotic properties. On the other hand, several reports suggest that under certain stress conditions or genetic manipulations Rhizobium cells can present genomic rearrangements. In search of frequent genomic rearrangements, we analyzed three Rhizobium strains under laboratory conditions that are not considered to cause stress in bacterial populations. DNAs from direct descendants of a single cell were analyzed in regard to the hybridization patterns obtained, using as probes different recombinant plasmids or cosmids; while most of the probes utilized did not show differences in the hybridization patterns, some of them revealed the occurrence of frequent genomic rearrangements. The implications and possible biological significance of these observations are discussed.

Reiterated DNA sequences in Rhizobium and Agrobacterium spp

Repeated DNA sequences are a general characteristic of eucaryotic genomes. Although several examples of DNA reiteration have been found in procaryotic organisms, only in the case of the archaebacteria Halobacterium halobium and Halobacterium volcanii [C. Sapienza and W. F. Doolittle, Nature (London) 295:384-389, 1982], has DNA reiteration been reported as a common genomic feature. The genomes of two Rhizobium phaseoli strains, one Rhizobium meliloti strain, and one Agrobacterium tumefaciens strain were analyzed for the presence of repetitive DNA. Rhizobium and Agrobacterium spp. are closely related soil bacteria that interact with plants and that belong to the taxonomical family Rhizobiaceae. Rhizobium species establish a nitrogen-fixing symbiosis in the roots of legumes, whereas Agrobacterium species is a pathogen in different plants. The four strains revealed a large number of repeated DNA sequences. The family size was usually small, from 2 to 5 elements, but some presented more than 10 elements. Rhizobium and Agrobacterium spp. contain large plasmids in addition to the chromosomes. Analysis of the two Rhizobium strains indicated that DNA reiteration is not confined to the chromosome or to some plasmids but is a property of the whole genome.

Genetic and biochemical identification of the glutamate synthase structural gene in Neurospora crassa

Neurospora crassa cells require glutamate synthase activity for growth under ammonium-limiting conditions. Despite the physiological importance of glutamate synthase, little is known about the genetics of its expression. To identify the glutamate synthase structural gene, we isolated three new mutants lacking this activity. All mutations are recessive to the wild-type allele and belong to the same complementation group as the previously described en(am)-2 (C24) mutation. Two lines of evidence indicate that en(am)-2 is the structural gene for glutamate synthase in N. crassa. The en(am)-2+ gene shows a gene dosage effect on enzyme activity, and some mutants lacking glutamate synthase activity have cross-reacting material. These data suggest that the mutations are located in the structural gene for N. crassa glutamate synthase.

Glutamine synthetase-constitutive mutation affecting the glnALG upstream promoter of Escherichia coli

The spontaneous gln-76 mutation of Escherichia coli (Osorio et al., Mol. Gen. Genet. 194:114-123, 1984) was previously shown to be responsible for the cis-dominant constitutive expression of the glnA gene in the absence of a glnG-glnF activator system. Nucleotide sequence analysis has now revealed that gln-76 is a single transversion T.A to A.T, an up-promoter mutation affecting the -10 region of glnAp1, the upstream promoter of the glnALG control region. Both, wild-type and gln-76 DNA control regions were cloned into the promoter-probe plasmid pKO1. Galactokinase activity determinations of cells carrying the fused plasmids showed 10-fold more effective expression mediated by gln-76 than by the glnA wild-type control region. Primer extension experiments with RNA from strains carrying the gln-76 control region indicated that the transcription initiation sites were the same in both the gln-76 mutant and the wild type.