Intraspecific variation in reproductive physiology and egg quality in the European Starling Sturnus vulgaris

Egg mass shows large intraspecific variation in birds and is repeatable within individuals. The mechanisms underlying this variation are unknown. We hypothesized that measures of egg quality (the mass of yolk protein, yolk lipid, and albumen protein) would be positively correlated with the plasma pools of the yolk precursor vitellogenin, and the masses of the oviduct, metabolic machinery (liver, heart, lungs, kidneys, gizzard, small intestine and pancreas), and endogenous stores of protein and lipid. We tested these predictions in European Starlings Sturnus vulgaris collected at the peak of egg production effort. In contrast to our predictions, both yolk protein and yolk lipid were negatively correlated with plasma vitellogenin levels. Albumen protein was positively related to oviduct mass, but other aspects of body composition failed to explain variation in egg quality. Hence, while we observed correlations between egg composition and peripheral systems (circulating precursor pools and the oviduct), we found no evidence that egg quality is determined by more general processes, i.e., the supply and processing of nutrients.     

Relationship of an unstable argG gene to a 5.7-kilobase amplifiable DNA sequence in Streptomyces lividans 66.

The relationship between an unstable argG gene and a 5.7-kilobase (kb) amplifiable DNA sequence in Streptomyces lividans 66 was investigated. Spontaneous, high-frequency Arg mutants deleted for this gene typically contain 200 to 300 copies of the tandemly reiterated sequence. A library of S. lividans 66 (strain 1326) wild-type genomic DNA was prepared in the vector lambda Charon 35. Chromosome walking over 44 kb established that argG is located 25 kb distant from a duplicated amplifiable DNA structure. A sequence was characterized, located farther distal from the amplifiable structure, containing strong homology with an internal sequence of the amplifiable DNA, which may have a role in the deletion of argG. Genetic mapping showed that argG and the 5.7-kb amplifiable sequence are linked to another unstable gene, determining chloramphenicol resistance (Camr) and that together these genes may be located in a silent chromosomal arc.     

Genetic instability and DNA amplification in Streptomyces lividans 66.

Streptomyces lividans 66 exhibits genetic instability, involving sequential loss of resistance to chloramphenicol (Cams) and subsequent mutation of argG. Associated with this instability is the amplification of a 5.7-kilobase (kb) amplified DNA sequence (ADS). We have characterized a second, independent pathway of genetic instability, involving sequential loss of resistance to tetracycline (Tets) followed by mutation in nitrogen assimilation (Ntr). We detected DNA amplification in many of these mutant strains, as well as other reiterations coresident with the 5.7-kb ADS in Cams Arg mutants. However, in contrast to the 5.7-kb ADS, none of the novel elements were observed to amplify at high frequency. The mutation of argG is due to a deletion, one endpoint of which is defined by the 5.7-kb ADS. This amplification derives from a structure, the tandemly duplicated amplifiable unit of DNA (AUD), present in the wild-type genome. We found that progenitor strains containing just a single-copy AUD failed to reproducibly generate amplification of this element in Cams argG mutants, and DNA deletion endpoints proximal to the element were found to be unspecific. These results suggest that a duplicated AUD structure is required for high-frequency amplification and that this reiteration can subsequently buffer the extent of deletion formation in the relevant chromosomal region.     

Aminoglycoside suppression at UAG, UAA and UGA codons in Escherichia coli and human tissue culture cells

Summary We have compared the suppression of nonsense mutations by aminoglycoside antibiotics inEscherichia coli and in human 293 cells. Six nonsense alleles of the chloramphenicol acetyl transferase (cat) gene, in the vector pRSVcat, were suppressed by growth in G418 and paromomycin. Readthrough at UAG, UAA and UGA codons was monitored with enzyme assays for chloramphenicol acetyl transferase (CAT), in stably transformed bacteria and during transient expression from the same plasmid in human 293 tissue culture cells. We have found significant differences in the degree of suppression amongst three UAG codons and two UAA codons in different mRNA contexts. However, the pattern of these effects are not the same in the two organisms. Our data suggest that context effects of nonsense suppression may operate under different rules inE. coli and human cells.     

Factors influencing genetic counseling attendance rate: a geographically based study

A study of factors influencing genetic counseling attendance rate has been conducted in the Bouches-du-Rh?ne area, in the south of France. In this area, a birth defects monitoring system (Eurocat n. 22) annually covers 23,000 births. All the genetic services are delivered by only one genetic center located in Marseilles, and the data collected are computerized. The comparison of these two data bases gives an opportunity to estimate the rate of genetic counseling attendance after the occurrence of an affected stillbirth or live birth. Among the parents of 358 infants born in 1983-84 in this area with a pathology requiring genetic counseling, 226 (63 per cent) attended the Genetic Center within the first year after birth. The rate of attendance is statistically higher (p less than 0.01) for the parents who had a stillbirth (78 per cent) than for those who had a live birth (57 per cent). It is also higher (p less than 0.01) for the Marseilles maternities group (68 per cent) than for the group outside Marseilles (50 per cent). The referral delays are also analyzed according to malformation etiology and to viability of the child by the eighth day of life. Besides evaluating a particular genetic center's effectiveness in diffusing information to the public concerned, this work shows that couples' request is strongly dependent on a psychological need.     

Assignment of the proton NMR spectrum of reduced and oxidized thioredoxin: sequence-specific assignments, secondary structure, and global fold

Complete proton assignments are reported for the 1H nuclear magnetic resonance (NMR) spectrum of Escherichia coli thioredoxin in the oxidized (with active-site disulfide bridge) and reduced (with two sulfhydryl groups) states. The assignments were obtained by using an integrated assignment strategy in which spin systems were identified from a combination of relayed and multiple quantum NMR techniques prior to sequential assignment. Elements of secondary structure were identified in each protein from characteristic nuclear Overhauser effects (NOE), coupling constants, and slowly exchanging amide protons. In both oxidized and reduced thioredoxin, approximately 33% of the 108 amino acid residues participate in a beta-sheet containing four major strands (three antiparallel and one parallel). A further short beta-strand is connected in a parallel fashion at the N-terminal end of the sheet. Two of the antiparallel beta-strands are connected by a 7-residue beta-bulge loop. Three helical segments, also containing approximately 33% of the amino acid residues, are well-defined in both oxidized and reduced thioredoxin. The remaining third of the molecule apparently consists of reverse turns and loops with little defined secondary structure. The global folds of oxidized and reduced thioredoxin are shown to be essentially identical. Both NOE connectivities and chemical shift values for the two proteins are very similar, except in the immediate vicinity of the active site where significant variations in the chemical shift indicate subtle conformational changes. While the overall fold of oxidized thioredoxin is the same in solution and in the crystalline state, some small differences in local conformation are apparent.     

Effects of DNase production, plasmid size, and restriction barriers on transformation of Vibrio cholerae by electroporation and osmotic shock

Attempts to transform wild type strains of V. cholerae with plasmid DNA by traditional osmotic shock methods were not successful. A mutant of V. cholerae that was deficient in extracellular DNase was transformed with plasmid DNA by osmotic shock, demonstrating directly that extracellular DNase is a major barrier to transformation of V. cholerae. Transformation of wild type and DNase-negative strains of V. cholerae was accomplished by electroporation. Efficiency of transformation by electroporation increased with field strength, decreased with plasmid size, and was relatively insensitive to changes in the electrolyte composition of the buffer as long as isotonic sucrose was present. Host-controlled modification/restriction systems also affected transformation efficiency in V. cholerae.     

Relation between the anion exchange protein in kidney medullary collecting duct cells and red cell band 3

Summary A membrane protein that is immunochemically similar to the red cell anion exchange protein, band 3, has been identified on the basolateral face of the outer medullary collecting duct (MCD) cells in rabbit kidney. In freshly prepared separated rabbit MCD cells, M.L. Zeidel, P. Silva and J.L. Seifter (J. Clin. Invest. 77:1682–1688, 1986) found that Cl^–/HCO ₃ ^- exchange was inhibited by the stilbene anion exchange inhibitor, DIDS (4,4-diisothiocyano-2,2-disulfonic stilbene), with aK ₁ similar to that for the red cell. We have measured the binding affinities of a fluorescent stilbene inhibitor, DBDS (4,4-dibenzamido-2,2-disulfonic stilbene), to MCD cells in 28.5 mM citrate and have characterized both a high-affinity site (K ₁ ^s =93±24 mM) and a lower affinity site (K ₂ ^s =430±260 nM), which are closely similar to values for the red cell of 110±51 nM for the high-affinity site and 980±200 nM for the lower affinity site (A.S. Verkman, J.A. Dix & A.K. Solomon,J. Gen. Physiol. 81:421–449, 1983). When Cl^– replaces citrate in the buffer, the two sites collapse into a single one withK ₁ ^s =1500±400 nM, similar to the singleK ₁ ^s =1200±200 nM in the red cell (J.A. Dix, A.S. Verkman & A.K. Solomon,J. Membrane Biol. 89:211–223, 1986). The kinetics of DBDS binding to MCD cells at 0.25 M^–1 are characterized by a fast process, =0.14±0.03 sec, similar to =0.12±0.03 sec in the red cell. These similarities show that the physical chemical characteristics of stilbene inhibitor binding to MCD cell band 3 closely resemble those for red cell band 3, which suggests that the molecular structure is highly conserved.