Search

This article establishes a context for secure information systems development as well as a set of models used to develop and apply a secure software production pedagogy. A generic system model is presented to support the system context development, and to provide a framework for discussing security relationships that exist between and among information systems and their applications. An asset protection model is tailored to provide a conceptual ontology for secure information system topics, and a stable logical framework that is independent of specific organizations, technologies, and their associated changes. This asset protection model provides a unique focus for each of the three primary professional communities associated with the development and operation of secure information systems. In this paper, a secure adaptive response model is discussed to provide an analytical tool to assess risk associated with the development and deployment of secure information systems, and to use as a security metric. A pedagogical model for information assurance curriculum development is then established in the context and terms of the developed secure information system models. The relevance of secure coding techniques to the production of secure systems, architectures, and organizational operations is also discussed.

Among the fertile sugar beet lines with nuclear sterility maintenance genes, rf, in a homozygous recessive state, sublines capable of reverting spontaneously at a high rate to sterility were identified. Of 24 related fertile sublines studied, 6 were found to spontaneously revert to sterility with a frequency of about 19%. Genetic analysis confirmed the cytoplasmic nature of spontaneously arising sterility. Reversion to sterility in these sublines was accompanied by alterations in the mitochondrial genome structure: loss of the autonomously replicating minicircle c (1.3 kb) and changes in the restriction patterns of high-molecular-weight mitochondrial DNA (mtDNA). Southern hybridixation analysis with cloned minicircle c as a probe revealed no integration of this DNA molecule into the main mitochondrial and nuclear genomes of the revertants. Comparative BamHI and EcoRI restriction analysis of the mtDNA from the sterile revertants and fertile parental subline showed that the spontaneous reversion is accompanied by extensive genomic rearrangement. Southern blot analysis with cloned α-subunit of F1-ATPase (atpA) and cytochrome c oxidase subunit II (COX II) genes as probes indicated that the changes in mtDNA accompanying spontaneous reversion to sterility involved these regions. The mitochondrial genomes of the spontaneous revertants and the sterile analogue were shown to be identical.

Variations in mitochondrial genome organization and in its expression between fertile, sterile sugar beet lines and fertile nuclear-restored plants were studied. Southern blot hybridization with COXI, COXII, COB and atpA mitochondrial genes as probes showed that changes in the mitochondrial genome organization of sterile lines are associated with variations in the location of COB, atpA and COXII, but not COXI. When the COXII and atpA genes were used as hybridization probes, differences in the primary structure of mitochondrial DNAs from sterile lines of different origin were revealed. Differences in the transcriptional patterns of the three mitochondrial genes (COXI, COXII and atpA) were observed between fertile and sterile sugar beet lines; COB was the only mitochondrial gene whose transcription was identical in both fertile and sterile cytoplasms. The dominant nuclear fertility restorer genes altered the transcriptional patterns of the COB and atpA without affecting those of the COXI and COXII genes; atp A expression was identical in fertile plants and nuclear-restored plants with sterile cytoplasm.

The higher-plant mitochondrial (mt) genome differs from the animal genome in many respects. The mt genomes of plants attain 2500 kb, but those of animals do not exceed 18 kb. The plant mt genomes are organised as multiple circular molecules and they contain, in addition to high molecular weight (HMW) DNA, low molecular weight (LMW) DNA, including plasmid-like molecules (Newton, 1988).