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Honighäuschen (Bonn) - Historecognition, broadly defined, spans the processes responsible for the regulation of the genetic integrity of self in the face of conspecific (allogeneic) and heterospecific (xenogeneic) nonself. The existence of precise historecognition systems in the invertebrates can be traced back to Bancroft's discovery in 1903 of ,strain specific regulation of colony fusion in the compound ascidian Botryllus schlosseri, and Wilson's report in 1907 of species-specific sponge re-aggregation. Despite this provocative history, invertebrate historecognition remained largely unexplored for over half a century, while studies of vertebrate immune systems prospered. Then, in the 1970's, interest in invertebrate his tore cognition grew once again, this time cast largely in terms of understanding the mechanisms and evolutionary history of vertebrate immunity. From our current understanding of vertebrate immunity and invertebrate historecognition, three generalizations about their relationships can be drawn. First, despite substantial knowledge about the genetics and molecular biology of cell recognition in the context of vertebrate immunity and to a lesser extent of invertebrate historecognition, the evolutionary relationships between invertebrate self/nonself recognition and vertebrate immune systems remain obscure. Second, although vertebrate allograft recognition is of dubious functional significance itself (because intergenotypic cellular contacts are unusual, except during fertilization and pregnancy), natural allografts occur frequently as sedentary invertebrates grow and compete for living space. It is now known that the operation of invertebrate his tore cognition systems can profoundly affect the outcomes of competitive interactions by mediating allogeneic aggressive behavior and somatic fusion.

Invertebrate Historecognition

$Honighäuschen (Bonn) - The study of the primary structure of nucleic acids, i. e. , the determination of the nucleotide sequence in ribosomal, transfer, and messenger types of RNA and in DNA, is an essential preliminary to the attempt to correlate the structures of these compounds with their functions. This is one of the most urgent problems in molecular biology, for until it is solved it is im possible to understand fully the mechanisms of fundamental living processes. Research has naturally tended to concentrate on the nucleic acids of smallest molecular weight, namely the transfer RNAs, and tremendous progress has been made in recent years in the unraveling of their structure. In 1958-1959, when structural investigation was still in its infancy, it was even doubted whether the structure of any transfer RNA could be deter mined. No methods of isolating homogeneous preparations were available, and it was uncertain whether the very slight physical and chemical differences between tRNAs of different specificity would be sufficient to allow successful fractionation. When the first enriched preparations were obtained, there arose the problem of whether it was possible to determine the nucleotide sequence having regard to the limited number of heterogeneous structural elements present in tRNA. These doubts were resolved in 1965, when the structure of the first nucleic acid, alanine-specific transfer RNA, was unraveled in Holley's laboratory.$