Amylase-binding as a discriminition among oral streptococci

The ability of 51 strains, belonging to Streptococcus sanguis, 'S. mitior', S. oralis and related groups, to bind salivary amylase was studied. Most strains were grouped according to their DNA-relatedness and then compared using 14 phenotypic tests. S. mitis, 'S. mitior' and three relatively new groups of strains ('CR', 'MGH' and 'Tufted mitior') bound salivary amylase, while strains of S. sanguis and S. oralis did not. The ability of strains to bind amylase or not was remarkably consistent within groups and the test proved to be reproducible, rapid and easy to perform. Combination of the amylase-binding test with 6 other conventional physiological tests allowed the construction of a dichotomous identification key which correctly identified 95% of strains for which genetic data was available. These findings suggest that the ability of organisms to bind salivary amylase could become a key test in identification schemes for certain oral streptococci.     

Characterization of the secondary structure and melting of a self-cleaved RNA hammerhead domain by 1H NMR spectroscopy.

We have completely assigned the extreme low-field ring-NH nuclear magnetic resonance spectrum of a self-cleaving RNA in the absence of magnesium ions by experiments involving sequential Overhauser enhancements between adjacent base pairs. These assignments substantiate the hammerhead secondary folding model proposed by Symons and co-workers for this class of self-cleaving RNA [Hutchins, C. J., Rathjen, P. D., Forster, A. C., & Symons, R. H. (1986) Nucleic Acids Res. 14, 3627-3640; Forster, A. C. & Symons, R. H. (1987) Cell 49, 211-220; Kneese, P., & Symons, R. H. (1987) in Viroids and Viroid-like Pathogens (Semancick, J. S., Ed.) pp 1-47, CRC Press, Boca Raton, FL]. No resonances due to tertiary base pairs could be identified in the low-field spectrum, and addition of MgCl2 to the sample did not produce additional resonances in this region of the spectrum.