Replisome pausing in mutagenesis

E. coli cells containing a temperature-sensitivednaE mutation, in the α-subunit of holoenzyme DNA polymerase III, do not survive at the restrictive temperature. Such cells may survive in the presence of thepcbA1 mutation, an allele of thegyrB gene. Such survival is dependent on an active DNA polymerase I. Evidence indicates that DNA polymerase I interacts directly in the replisome (REP·A). Despite normal survival for cells using thepcbA replication pathway after some type of DNA damage, we have noted a failure of damage-induced mutagenesis. Here we present evidence supporting a model of replisome pausing in cells dependent upon thepcbA replication pathway. The model argues that the (REP·A) complex pauses longer at the site of the lesion, allowing excision repair to occur completely. In the normal replication pathway (REP·E) bypass of the lesion occurs, fixing the mutation.     

Ruddy turnstones Arenaria interpres rapidly build pectoral muscle after raptor scares

To cope with changes in the environment, organisms not only show behavioural but also phenotypic adjustments. This is well established for the digestive tract. Here we present a first case of birds adjusting their flight machinery in response to predation risk. In an indoor experiment, ruddy turnstones Arenaria interpres were subjected to an unpredictable daily appearance of either a raptor or a small gull (as a control). Ruddy turnstones experiencing threat induced by a flying raptor model, longer than after similar passage by the gull model, refrained from feeding after this disturbance. Pectoral muscle mass, but not lean mass, responded in a course of a few days to changes in the perceived threat of predation. Pectoral muscle mass increased after raptor scares. Taking the small increases in body mass into account, pectoral muscle mass was 3.6% higher than aerodynamically predicted for constant flight performance. This demonstrates that perceived risk factors may directly affect organ size.     

Stability of Lanatoside C content in thein vitro propagatedDigitalis lanata clones

In vitro culture was established from shoot tips ofDigitalis lanata cotyledonous plants. The propagated plant material was rooted, transplanted into soil and grown under field conditions. Lanatoside C content was determined in a total of 20 clones and statistically evaluated by means of variance analysis of unequal-sized samples.In vitro clonal propagation ofD. lanata was found not to affect lanatoside C content. Drug level was dependent on a plant genotype.     

Book Review

International Journal of Primatology -     

Somatic hybrid plants produced by electrofusion between dihaploid potatoes: BF15 (H1), Aminca (H6) and Cardinal (H3)

In order to regenerate somatic hybrids, mesophyll protoplasts from a dihaploid potato, BF15 (H1), were electrofused with those from two other dihaploid clones, Aminca (H6) and Cardinal (H3). Determination of the ploidy level by flow cytometry showed that 10% of plants regenerated from the fusion experiment with BF15 + Aminca were diploids, 14% triploids, 63% tetraploids and very few were mixoploids or had a higher ploidy level. Using morphological markers and vigour in plant growth, we were able to recover a total of 24 somatic hybrid plants, respectively 20 and 4 hybrids (accounting for 12% and 13% of regenerants) from the fusions BF15 + Aminca and BF15 + Cardinal. Most of the somatic hybrids were at the expected tetraploid level (2n=4x=48). The hybrid nature was confirmed by examining isoenzyme patterns for malate dehydrogenase (MDH) and isocitrate dehydrogenase (ICD).     

The localisation of an Mr 74,000 major chromatin antigen on native salivary chromosomes of Drosophila melanogaster

An antigen making a major contribution to the immune response to Drosophila melanogaster chromatin resides primarily on a nonhistone charge-class family of proteins of Mr 74,000. Immunofluorescence detects this antigen at interbands, puffs and diffuse bands of D. melanogaster salivary chromosomes isolated without exposure to acid fixatives, and on nucleoplasmic ribonucleoprotein droplets. In the electron microscope, gold labelling reveals the binding of monoclonal antibodies specific for the antigen at chromosomal loci generally bearing putative ribonucleoprotein (RNP) particles. However, the locus 3C 11–12 is remarkable in that it bears putative RNP particles but is virtually unlabelled, suggesting protein specificity at different active loci.