Co-segregation of a gene encoding a deletion ligand for Tcrb-V3+ T cells with Mtv-3

A gene encoding the endogenous superantigen Mls^c, which deletes Tcrb-V3⁺ T cells in the NOD inbred mouse strain, was found to co-segregate with Mtv-3 on chromosome 11. This identifies a fourth gene encoding a deletion ligand for Tcrb-V3⁺ T cells and extends recently published observations in support of the hypothesis that a number of endogenous superantigens are the products of Mtv proviruses. Address correspondence and offprint requests to : K. Tomonari.     

DNA polymerase-primase from embryos of Drosophila melanogaster. The DNA polymerase subunit

The DNA polymerase-primase from Drosophila melanogaster has been separated into its constituent polymerase and primase subunits by sedimentation in glycerol gradients containing 50% ethylene glycol. Both activities have been obtained in good yield. The properties of the 182-kDa polymerase subunit are similar to those of the intact four-subunit enzyme. However, there are three significant differences. (i) The polymerase activity of the 182-kDa subunit shows an increased thermolability; (ii) the pause sites during replication of singly primed, single-stranded circular DNA by the 182-kDa subunit are altered; and (iii) unlike the intact enzyme, the 182-kDa subunit is highly processive in the presence of the single-stranded DNA-binding protein of Escherichia coli.     

Rapid determination of antimicrobial susceptibility patterns ofListeria monocytogenes isolates by the autobac AIS and MIC procedures

A total of 34 isolates ofListeria monocytogenes were tested against ampicillin, cephalothin, chloramphenicol, erythromycin, tetracycline, and penicillin-G using the Autobac 3-h AIS and the Autobac 5-h MIC procedures. The results were compared to susceptibility category interpretations and MICs determined using the Sceptor system. With the Sceptor System, all isolates were interpreted to be moderately susceptible to ampicillin and penicillin-G, and susceptible to the four other antibiotics. With the Autobac AIS, all isolates were interpreted to be susceptible to all the antibiotics except penicillin-G. All but one of the 34 isolates were interpreted to be resistant to penicillin-G with the Autobac AIS test. The remaining isolate was interpreted to be indeterminant. The Autobac AIS test was unsatisfactory for determining the susceptibility ofL. monocytogenes isolates to penicillin-G. The Autobac MIC results correlated well with the MIC results of the Sceptor system provided that the Autobac was programmed as though it were testing enterococci. The Autobac MIC reported penicillin-G MICs in units per milliliter and required the use of a conversion factor to obtain micrograms per milliliter, and did not allow for the testing of erythromycin. The Autobac MIC susceptibility category interpretations must not be used, as they were derived from an outdated susceptibility standard. The Autobac MIC test may be used if the limitations given above are observed.     

Isolation of single taste cells from lingual epithelium

A method is described for obtaining large numbers of isolatedtaste cells with identified polarity from lingual epithelium.The procedure involves incubating lingual epithelium in collagenase,staining the apical surface with fluorescein-conjugated wheatgerm agglutinin (FTTC-WGA), peeling non-gustatory surface epitheliumfrom the underlying taste buds and connective tissue, and dissociatingisolated taste buds with Ca²⁺-free saline. Isolated taste cellsretain their characteristic morphology for at least 30 min afterdissociation, and the apical specialization can be identifiedas a single patch of fluorescence usually located at the tipof an elongate process. Isolated taste cells are amenable tostudy with the patch-clamp technique, and whole-cell patch-clamprecordings show that isolated taste cells have membrane propertiessimilar to taste cells of intact lingual epithelium. Evidenceis presented that FITC-WGA staining does not alter the voltage-dependentionic currents of the taste cell membrane.     

Use of a root assessment tray for the detection of take-all on lateral roots of wheat seedlings

A root assessment tray was designed for the meticulous assessment of take-all on wheat seedling roots from soil bioassays. Subsequently, the detection of lateral root infections (in addition to the more obvious infections on main axes of seminal roots) resulted in increased estimates of propagule numbers of the take-all fungus (Gaeumannomyces graminis var.tritici) for 196 of the 368 soil samples bioassayed in a field study conducted in Western Australia between 1984 and 1986.     

Reduction of Take-all Inoculum by Rotation with Lupins, Oats or Field Peas

The feasibility of use of lupins, oats and field peas as alternative rotation crops to reduce inoculum of the take-all fungus (Gaeumannomyces graminis var. tritici) (under Western Australian field conditions) and disease in following wheat was investigated with a one year field trial, the soil from which was used in two succeeding pot experiments. The possible mechanisms of reduction of inoculum and disease by these crops were examined testing the soil for pathogen and disease suppression. Rotation with lupins or oats for two seasons reduced (P <0.05) inoculum of the take-all fungus and lupins, oats or field peas reduced (P <0.05) disease in following wheat. Lupins alone reduced inoculum and disease, (P <0.1) after one season. No apparent suppression of the pathogen in the absence of host plants was recorded after one season of rotation, but after two seasons, lupins, oats or field peas all suppressed (P <0.02) growth of the pathogen within soil. However only field pea soil suppressed take-all in comparison with the wheat control. Although after two seasons all rotation crops were effective in reducing inoculum and disease the mechanisms of reduction appear to differ between the rotation crops used in this study.