Monitoring the integrity of self: biology of MHC-restriction of virus-immune T cells

All available evidence indicates that the cytotoxic thymus-derived lymphocyte (T cell), which is lytic for virus-infected target cells in vitro, is also the effector in cell-mediated immunity in vivo. Such T cell show two orders of specificity: for the virus in question, and for a particular self major histocompatibility complex (MHC) glycoprotein. Recirculating T cells amy thus be considered to survey the integrity of self, the self components involved being the cell-surface structures that are recognized as foreign during graft rejection. Virus-infected liver cells are apparently eliminated in much the same way as a transplanted organ. The necessary balance between self-tolerance (absence of autoreactivity) and self-monitoring effector T cell function seems to be established during the process of differentiation in thymus. The molecular nature of the underlying recognition events is, as yet, obscure.     

Genetic studies on capsid-length determination in bacteriophage T4. I. Isolation and partial characterization of second-site revertants of a gene 23 mutation affecting capsid length.

The T4 mutation ptg19-80 affects the mechanism of capsid-length determination. It is located in gene 23, which encodes the major structural protein of the capsid. The mutation results in the production of abnormal-length capsids in high frequencies. This paper describes the isolation and partial characterization of second-site revertants of ptg19-80. In the course of their analysis, it was discovered that ptg19-80 is itself a double mutation consisting of a gene 23 mutation (ptg19-80c), which causes the morphogenetic defect, and a suppressor mutation located near the lysozyme gene. Phenotypic characterization of nine pseudo-wild-type revertants of this double-mutation revealed that these revertants all produced lower frequencies of abnormal capsids than did ptg19-80. Seven of these revertants were shown to contain two suppressor mutations, one mapping in or near gene 22 and done mapping in or near gene 24. Both mutations were required for suppression. These suppressors displayed no discernible phenotype in the absence of ptg19-80c.     

Estimation and fractionation of the essentially unbranched (amylose) and branched (amylopectin) components of starches with concanavalin A

Conditions have been devised for the quantitative precipitation of the branched fraction in starches by concanavalin A and the enzymic estimation of the - -glucan in this and the soluble components. For some starches, such as those from cereal and high-amylose pea seeds, the percentage of branched fraction determined by this procedure was higher than that calculated by deducting from one hundred the apparent amylose content as measured by potentiometric iodine titration, suggesting a method for estimating the content of material having an atypical structure in the whole starch. The procedure has been adapted to provide a preparative method of separating amylose and amylopectin fractions. It efficiently separated these in starches that cannot be fully fractionated by complexing with 1-butanol, such as those from high-amylose pea seeds and tobacco leaves.     

The Effect of Farmer Attitudes and Objectives on the Heterogeneity of Farm Attributes and Management in Switzerland

Identifying and interpreting the heterogeneity of farmer behaviour is becoming increasingly important in support of policy- and decision-making goals. This paper explores whether observed differences in farming practices can be interpreted from the heterogeneity of farmer behaviour. Farmer attitudes and objectives were analysed using a combination of principal components and cluster analysis applied to responses to statements in a telephone-based survey. Respondents were classified into four profiles; business-oriented, lifestylers, multifunctionalists and traditionalists. Each profile differed in terms of farm management practices, the amount of land farmers either managed or owned, the existence of successors and the importance placed on household members in providing information. The results suggest that knowledge of farmer behavioural profiles could support more targeted policy development that accounts for alternative farmer goals. However, similarities were also found between the profiles, suggesting that farmer behaviour would be better interpreted as a dynamic set of identities, rather than as static profiles.