Transient electric birefringence of the bacteriophages T3 and T7

Electric birefringence measurements of suspensions of T3 and T7 bacteriophages in 10^?2 M phosphate buffer, pH 6.9, show that there is a difference in their rotational diffusion coefficient. The values corrected to 25°C and water viscosity are D_25,w = 4630 ± 130 sec^?1 and D_25,w = 5290 ± 260 sec^?1 for T3 and T7, respectively. The value obtained from shell model calculations (according to Filson and Bloomfield) is D_25,w = 4500 ± 600 sec^?1. The apparent permanent dipole moments are 4.5 × 10^?26 C·m and 1.7 × 10^?26 C·m for T3 and T7, respectively. For both phage particles the intrinsic optical anisotropy is +7.2 × 10^?3. It is shown that this anisotropy is mainly due to the DNA molecule inside the head of the phage. Its positive value means that there exists an excess orientation of the DNA helix perpendicular to the symmetry axis of the particle. For T7 an unexpectedly large increase of Δn_s and K_sp occurs at a glycerol concentration of about 30% (v/v). This increase is interpreted as being caused by a change of the shape of the particle and/or a change in the secondary structure of the DNA inside the head of the bacteriophage.     

Different restriction of bacteriophages T3 and T7 by P1-lysogenic cells and the role of the T3-coded SAMase.

The intracellular growth of the phages T3 and T7 is restricted in the presence of the Escherichia coli prophage P1. Phage T3 has a higher ability to express its genome and to damage the host cell than T7. This partial protection of T3 against P1 restriction is due to the T3-coded SAMase, an enzyme which degrades S-adenosylmethionine, the cofactor of the P1 restriction endonuclease. Since we did not observe DNA cleavage in vivo, we conclude that the in vivo action of the P1 nuclease is limited to a SAM-dependent repressor-like binding to T3 and T7 DNA, while further reactions with the DNA (modification vs cleavage) are blocked.     

Active protection by bacteriophages T3 and T7 againstE. coli B-and K-specific restriction of their DNA

Summary The bacteriophages T3 and T7 are not modified and restricted byE. coli strains with different host specificity (E. coli B, K, O) in vivo. The phages code for a gene product with the ability toovercomeclassicalrestriction (ocr):ocr ^– mutants are subject to modification and restriction via DNA methylation vs cleavage. The T3 genome possesses recognition sites for the restriction endonuclease R.EcoB which, unless the DNA is B-specifically modified, trigger 5–7 DNA cleavages. Theocr gene function of T3 and T7 is located within the gene 0.3 region of these phages and is not identical with thesam (SAMase) function of T3. The mechanisms ofocr protection remains unclear, while it is certain that this protection by the gene 0.3 protein is exerted in the infected cell and not through over-all modification in the preceding growth cycle of the phage.     

Genetic and physical mapping in the early region of bacteriophage T7 DNA.

A detailed physical map of the early region of bacteriophage T7 DNA has been constructed. This map contains: locations for all the cuts made by the restriction endonucleases HindII, HpaII, HaeIII and HaeII, and many of the cuts by HhaI; the approximate end points for each of 61 different deletions; initiation sites and the termination site for RNAs made by Escherichia coli RNA polymerase; an initiation site for RNA made by T7 RNA polymerase; the five primary RNase III cleavage sites of the early region; and the coding sequences for perhaps nine different early proteins. Virtually all of the non-overlapping coding capacity of the five early messenger RNAs is used, except for untranslated stretches of perhaps 30 or so nucleotides at the ends. It seems likely that each of the nine early proteins is made from its own ribosome-binding and initiation site. The mapped restriction cuts provide fixed reference points, and allow DNA fragments containing specific genetic signals to be identified and isolated.The nucleotide sequences around the ends of three different T7 deletions have been determined. Each deletion eliminated a segment of DNA between repeated sequences of seven, eight or ten base-pairs, located 578 to 2100 base-pairs apart in the wild-type sequence. In each case, one copy of the repeated sequence was retained in the deletion mutant. This is consistent with the deletions having arisen by a genetic crossover between the repeated sequences. The approximate frequency of genetic recombination per base-pair has been estimated within two early genes; in both cases, the value was close to 0.01% recombination per base-pair, consistent with the value expected from the total length of the T7 genetic map. Genetic recombination between non-overlapping deletions appears to be severely depressed when the distance between the deletions is closer than about 40 to 50 base-pairs, but recombination between a point mutation and a deletion does not appear to be similarly depressed. This suggests that efficient genetic recombination in T7 may require a base-paired “synapse” of some minimum size between the recombining DNA molecules.     

Exercise-induced pyruvate dehydrogenase activation is not affected by 7 days of bed rest

To test the hypothesis that physical inactivity impairs the exercise-induced modulation of pyruvate dehydrogenase (PDH), six healthy normally physically active male subjects completed 7 days of bed rest. Before and immediately after the bed rest, the subjects completed an oral glucose tolerance test (OGTT) and a one-legged knee extensor exercise bout [45 min at 60% maximal load (W(max))] with muscle biopsies obtained from vastus lateralis before, immediately after exercise, and at 3 h of recovery. Blood samples were taken from the femoral vein and artery before and after 40 min of exercise. Glucose intake elicited a larger (P ≤ 0.05) insulin response after bed rest than before, indicating glucose intolerance. There were no differences in lactate release/uptake across the exercising muscle before and after bed rest, but glucose uptake after 40 min of exercise was larger (P ≤ 0.05) before bed rest than after. Muscle glycogen content tended to be higher (0.05< P ≤ 0.10) after bed rest than before, but muscle glycogen breakdown in response to exercise was similar before and after bed rest. PDH-E1α protein content did not change in response to bed rest or in response to the exercise intervention. Exercise increased (P ≤ 0.05) the activity of PDH in the active form (PDHa) and induced (P ≤ 0.05) dephosphorylation of PDH-E1α on Ser2?3, Ser2?? and Ser3??, with no difference before and after bed rest. In conclusion, although 7 days of bed rest induced whole body glucose intolerance, exercise-induced PDH regulation in skeletal muscle was not changed. This suggests that exercise-induced PDH regulation in skeletal muscle is maintained in glucose-intolerant (e.g., insulin resistant) individuals.     

In synchronized pigs, the duration of ovulation is not affected by insemination and is not a determinant for early embryonic diversity

The duration of ovulation (i.e., the time interval between the ovulation of the first and the last follicle in a sow during an estrus) is said to be related to embryonic diversity, which in turn is related to embryonic mortality. The relationship between the duration of ovulation and within-litter early embryonic diversity and the influence of insemination on the duration of ovulation were studied. To determine whether ovulation assessment (transrectal ultrasonography) influenced early embryonic development, control sows were not scanned. Multiparous cyclic sows with an exogenously induced estrus were used. Ovulation detection by means of transrectal ultrasonography did not influence fertilization rate, accessory sperm count, early embryonic development or early embryonic diversity, and, therefore, ultrasonography appears to be a worthwhile method for studying the time and duration of ovulation. Insemination did not influence (P>0.05) the duration of ovulation, in sows which ovulated between 39 and 49 hours after hCG injection. The duration of ovulation (mean+/-SD(range)) was 2.4+/-0.7 (1.1 to 4.0) hours in 15 sows which were artificially inseminated at 22 and 30 hours after hCG injection. In 8 noninseminated sows, the duration of ovulation was 2.3+/-0.5 (1.5 to 3.3) hours. The duration of ovulation was not related to embryonic diversity (SD of the number of nuclei or the number of cell cycles of embryos in a litter) at 114 to 121 hours after ovulation. Thus, a difference of up to 3 hours in the duration of ovulation does not seem to be an important determinant of variation in embryonic diversity between sows.