-the only expedient way to run a biological documentation system is to keep the data recording so simple that no specialists are required for encoding; -a research documentation system will only be attractive to the scientist if it provides both the opportunity to carry out individual searches and also a continuing service in the form of SDI; -a research documentation will only remain up-to-date if the system is controlled by the research department, and if the scientist whose research results are documented continually collaborates in its extension and maintenance. In cooperation with the department

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The structure of the extracellular polysaccharide from Rhizobium meliloti, a microsymbiont in the nitrogen fixing symbiosis, has been investigated. The polysaccharide contains a terminal @-D-glucopyranosyl group with pyruvic acid ketalically linked to its 4 and 6 positions. After removal of this substituent from the methylated polysaccharide the four sugar residues in the side chain were removed sequentially by specific degradations; each of these steps involved oxidation, p-elimination by treatment with base, and, when necessary, acid hydrolysis under mild conditions. The result of each degradation was followed by trideuteriomethylation, hydrolysis, and analysis of the product by GLC/MS. The sequence of the sugar residues in the main chain was determined using a modified Smith degradation in which the polyalcohol, obtained after periodate oxidation-borohydride reduction, was methylated before the mild acid hydrolysis. As a result of these studies, it is concluded that the polysaccharide is composed of octasaccharide repeating units with the structure 25.Biosynthetic and structural studies have revealed that many bacterial polysaccharides are composed of oligosaccharide repeating units* and the largest of these which have been conclusively demonstrated are hexasaccharide repeating units (cf. ref 2-4). There is strong justification for this occurrence of small repeating units since larger ones would require more complex systems of enzymes for their biosynthesis. Despite this, however, preliminary studies on the extracellular polysaccharide from Rhizobium meliloti have indicated that it should either be composed of octasaccharide repeating units or have a less regular s t r~c t u r e .~,~ We now report the structural elucidation of this polysaccharide, using specific degradations.

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