Evaluation of sexual behaviour in rams in relation to their reproductive capacity

The objective of the study was to determine the individual differences in sexual activity of rams. In total, 374 observations were made on 17 rams (22 for each ram). The average duration of mating for all rams was 70.9 s, ranging from 30.0 to 166.7 s for particular rams. The average duration of mating for a group of ten more active rams (MAR) was 49.3 s, while for a group of seven less active rams (LAR) it was 101.8 s, the difference being highly significant. Significant differences were also found with respect to the average number of mounts per ejaculation, both between individual rams (mean 2.36) and between group MAR (2.20) and LAR (2.60). The percentage of failure, defined as copulations without ejaculation, was significantly higher in group LAR (11.1%) than in group MAR (2.5%), indicating that the rams of group MAR copulate much more efficiently than the other males. The lambing results obtained from service during the first oestrus did not show significant differences between groups MAR and LAR, neither with respect to their fertility nor to the lambing rate.     

Expression and reconstitution of a biologically active human interferon-gamma receptor in hamster cells

We report the expression of the human interferon-gamma (Hu-IFN-gamma) receptor from a cDNA clone in an animal cell where both stable expression of the cloned receptor as well as its biological activity is demonstrated for the first time. Biological activity of the receptor (i.e. expression of surface histocompatibility antigens in response to human interferon-gamma) requires the presence of human chromosome 21 demonstrating the requirement for at least one other species-specific factor in the modulation of receptor action. This system should now facilitate delineation of regions involved in the binding of human interferon-gamma and receptor signal transduction.     

Pentapeptide repeat protein QnrB1 requires ATP hydrolysis to rejuvenate poisoned gyrase complexes

DNA gyrase, a type II topoisomerase found predominantly in bacteria, is the target for a variety of ‘poisons’, namely natural product toxins (e.g. albicidin, microcin B17) and clinically important synthetic molecules (e.g. fluoroquinolones). Resistance to both groups can be mediated by pentapeptide repeat proteins (PRPs). Despite long-term studies, the mechanism of action of these protective PRPs is not known. We show that a PRP, QnrB1 provides specific protection against fluoroquinolones, which strictly requires ATP hydrolysis by gyrase. QnrB1 binds to the GyrB protein and stimulates ATPase activity of the isolated N-terminal ATPase domain of GyrB (GyrB43). We probed the QnrB1 binding site using site-specific incorporation of a photoreactive amino acid and mapped the crosslinks to the GyrB43 protein. We propose a model in which QnrB1 binding allosterically promotes dissociation of the fluoroquinolone molecule from the cleavage complex.