Complexity, contingency, and criticality.

Complexity originates from the tendency of large dynamical systems to organize themselves into a critical state, with avalanches or "punctuations" of all sizes. In the critical state, events which would otherwise be uncoupled become correlated. The apparent, historical contingency in many sciences, including geology, biology, and economics, finds a natural interpretation as a self-organized critical phenomenon. These ideas are discussed in the context of simple mathematical models of sandpiles and biological evolution. Insights are gained not only from numerical simulations but also from rigorous mathematical analysis.

Minimal epitopes expressed in a recombinant polyepitope protein are processed and presented to CD8+ cytotoxic T cells: implications for vaccine design.

The epitopes recognized by CD8+ cytotoxic T lymphocytes (CTL) are generated from cytosolic proteins by proteolytic processing. The nature of the influences exerted by the sequences flanking CTL epitopes on these processing events remains controversial. Here we show that each epitope within an artificial polyepitope protein containing nine minimal CD8+ CTL epitopes in sequence was processed and presented to appropriate CTL clones. Natural flanking sequences were thus not required to direct class I proteolytic processing. In addition, unnatural flanking sequences containing other CTL epitopes did not interfere with processing. The ability of every CTL epitope to be effectively processed from a protein containing only CTL epitopes is likely to find application in the construction of recombinant polyepitope CTL vaccines.

Contrasting complexity of two rust resistance loci in flax.

DNA probes from the L6 rust resistance gene of flax (Linum usitatissimum) hybridize to resistance genes at the unlinked M locus, indicating sequence similarities between genes at the two loci. Genetic and molecular data indicate that the L locus is simple and contains a single gene with 13 alleles and that the M locus is complex and contains a tandem array of genes of similar sequence. Thus the evolution of these two related loci has been different. The consequence of the contrasting structures of the L and M loci on the evolution of different rust resistance specificities can now be investigated at the molecular level