Dimeric chromenes and mixed dimers of a chromene with euparin from Encelia canescens

The investigation of Encelia canescens afforded, in addition to several known compounds, four new dimeric p-hydroxyacetophenone derivatives, two epimeric chromene dimers and two epimeric mixed dimers of euparin and encecalin. Furthermore, derivatives of tremetone and of encecalin were present. The structures were elucidated hy high field ¹H NMR spectroscopy.     

Base excision repair in the thermophile Thermus sp. strain X-1.

The thermophile Thermus sp. strain X-1, grown at 70 degrees C, contains uracil-DNA glycosylase and apurinic endonuclease activities, both of which are known to have roles in the repair of DNA damaged by heat. Both of these activities have temperature optima of about 70 degrees C. However, neither of these activities is present in quantities significantly greater than that found in Escherichia coli grown at 37 degrees C. Therefore, it appears that thermophilic organisms may not contain greatly elevated levels of the enzymes thought to be involved in the repair of DNA damaged by heat.