Direct and correlated responses to selection for weaning weight,post-weaning weight gain and six-week weight in mice

Summary Four lines of mice were formed from a common base population and selected for 37 generations for either increased 3-week weight (weaning weight), 6-week weight, 3–6 week gain, or maintained as a randomly bred control line. Realised heritability estimates for short-term (long-term) responses were 0.33±0.20 (0.07±0.10), 0.46±0.14 (0.26±0.09), 0.36±0.14 (0.24±0.11) for 3-week weight, 6-week weight and 3–6 week gain, respectively. Realised genetic correlations estimated from short-term (long-term) responses were 0.23±0.08 (0.35±0.10) between 3-week weight and 3–6 week gain; 0.82±0.04 (0.58±0.08) between 3-week weight and 6-week weight; and 0.81±0.04 (0.97±0.04) between 3–6 week gain and 6-week weight. The genetic correlation between 3-week weight and 6-week weight was asymmetric with a greater correlated response for 3-week weight when selecting for 6-week weight (1.06) than vice versa (0.63).     

Thymidine-kinase activity of cultured cells from individuals with inherited galactokinase deficiency

Cells of a person homozygous for galactokinase deficiency and of her heterozygous parents were found to be deficient in the enzyme thymidine kinase. The decrease in thymidine-kinase activity may be the result of a qualitative alteration in the enzyme molecule. This is reflected in the apparent alteration in the sensitivity of the enzyme to trifluorothymidine. It is suggested that this relationship between the galactokinase and thymidine kinase is not fortuitous but a reflection of their interdependence as found previously in the Chinese hamster.     

A continuous-flow, rapid-mixing, photolabeling technique applied to the acetylcholine receptor

A continuous-flow technique is described in which a photoaffinity label, membrane rich in acetylcholine receptor, and various effectors are rapidly mixed, passed through a delay tube, through a tube in which they are irradiated, and are collected in a tube containing quencher. Delay times as short as 20 ms between mixing and photolysis are achievable. Because the flow is continuous, milliliter volumes of membrane can be labeled in a single run, which is convenient for the analysis of both the functional effects and sites of photolabeling. Using this technique, we have found that receptor in its transitory, active state, in which the channel is open, is more susceptible to photolabeling by the noncompetitive inhibitor analog [3H] quinacrine azide than is receptor in either its resting or desensitized states, in which the channel is closed. This technique should prove generally useful for the photolabeling of transient conformational states of macromolecules.     

Genetic variance and drift in selfed and intermated populations derived from backcrossing

Summary The genetic variance among random-mated lines derived from backcrossing (BC_gS₁ lines) depends upon the backcross generation (g) and the number (n) of BC_gF₁ plants crossed in generations 1 through g. There is little effect of n on genetic variance for n > 6. The genetic variance among BC_gF₂-derived lines is greater than that among BC_gS₁ lines for all g. If either BC_gF₂-derived or BC_gS₁ lines are used as a base population for recurrent selection, 8, 16, 32, and 64 BC₁F₁, BC₂F₁, BC₃F₁, and BC₄F₁ plants, respectively, should be used to avoid loss of donor alleles to drift.Joint contribution of USDA-ARS and Journal Paper No. J-11224 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2471Formerly Research Geneticist, USDA-ARS, Ames, Iowa, USA     

Comparison of aldolase isozymes in placenta, HeLa cells, and human fibroblast cultures

The aldolase specific activity of the human carcinoma cell line, HeLa, against fructose 1,6-diphosphate as substrate is 4- to 5-fold greater than the specific activity of diploid human fibroblast cultures derived from skin and lung. HeLa aldolase is isozyme is predominantly the A type and its substrate preferences resemble human placenta. These findings provide further support for the oncofetal enzyme consitution of HeLa cells.     

Different effects of inhibitors on two mutants of Escherichia coli K12 affected in the Fo portion of the adenosine triphosphatase complex.

The effects of the inhibitors dicyclohexyl-carbodiimide (DCCD), bathophenanthroline and tertiary octylcatechol, on some enzyme activities in membranes from strains of Escherichia coli carrying mutations in the uncB or uncC genes have been studied. Membranes prepared from uncC mutants retain a normal DCCD-sensitive Mg2+-stimulated adenosine triphosphatase (Mg-ATPase) activity whereas in uncB mutants this enzyme activity is insensitive to DCCD. The membrane-bound Mg-ATPase activity from the uncC mutant strain, as compared with that from the normal strain, is only partially sensitive to the inhibitors bathophenanthroline or tertiary-octylcatechol. Both of these inhibitors stimulate the membrane-bound Mg-ATPase from uncB mutant strains. A DCCD-insensitive Mg-ATPase activity is found in the cytoplasmic fraction following cell disruption of either the uncB or the uncC mutants. The lipophilic chelators bathophenanthroline and tertiary-octylcatechol stimulate the activity of the 'soluble' Mg-ATPase in the uncB mutant but partially inhibit the activity in the uncC mutant. The NADH oxidase activities in membranes from both mutant and normal strains are strongly inhibited by tertiary-octylcatechol and bathophenanthroline but not by DCCD.     

Application of immunofluorescence to the establishment of an Encephalitozoon cuniculi-free rabbit colony.

Serologic screening of a rabbit breeding colony over a 9-month period showed that all 9-week-old rabbits with Encephalitozoon cuniculi infection were born of E cuniculi-infected does. This observation, obtained from studies on 395 young rabbits, suggested that transmission of infection is either transplacental or the result of close contact soon after birth. On this basis, 16 young healthy rabbits, seronegative to E cuniculi, were isolated and tested at 2-week intervals for antibodies to E cuniculi. In the first 2 months, seven rabbits showed indications of developing antibodies to E cuniculi and were immediately removed from the colony. The remaining rabbits along with their 52 offspring were tested for serum antibodies for a further 16 months and no rabbit became seropositive. Eight months after establishment of the colony, three does, one buck and six 12-week-old rabbits were killed. Macroscopic and extensive histologic and immunofluorescence examinations failed to reveal any evidence of infection with E cuniculi. These results showed that serological screening for E cuniculi infection by immunofluorescence is a simple yet adequate procedure for establishing a rabbit colony free of encephalitozoonosis.     

Protein synthesis by hybrid ribosomes reconstructed from rabbit reticulocyte ribosomal core-particles and amphibian or fungal split-proteins.

It was shown that high-salt (2.75 M-NH4Cl/69mM-MgCl2) shock treatment at 0 degrees C of the larger subparticles (L-subparticles) of rabbit, Xenopus laevis and Neurospora crassa cytoplasmic ribosomes yielded split-protein fractions that were not only functionally equivalent but also interchangeable. Thus, although the remaining core-particles were inactive in both the puromycin reaction and in poly(U)-directed polyphenylalanine synthesis, activity was restored when they were combined with either homologous or heterologous split-protein fractions. This technique was used to prepare active hybrid L-subparticles, e.g. rabbit cores/N. crassa split-proteins, and also active hybrid ribosomes, e.g. rabbit smaller subparticle/X. laevis core-particle/rabbit split-proteins. Rabbit and X. laevis split-protein fractions labelled with 14C by reductive methylation with [14C]formaldehyde and sodium cyanoborohydride were both shown to bind to rabbit core-particles in approximate correlation with the degree of re-activation. The split-protein fractions of rabbit and X. laevis L-subparticles were analysed by two-dimensional and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The molecular weights (measured in sodium dodecyl sulphate gels) of the split-proteins of rabbit and X. laevis L-subparticles were found to be similar. These results demonstrate that the peptidyltransferase active centre of cytoplasmic ribosomes of eukaryotes has components that are interchangeable over a wide evolutionary range. Evidently the essential molecular architecture of the active centre is highly conserved.