Regulation of homocysteine metabolizing enzymes in Aspergillus nidulans

Summary Mutants of Aspergillus nidulans blocked in the main pathway of cysteine synthesis show an elevated level of the enzymes involved in the synthesis of cysteine from homocysteine i.e. cystathionine -synthase and -cystathionase and a depressed level of homocysteine methyltransferase. This results in a considerable change in the sulfur amino acids pool as compared to the wild type. Upon addition of cysteine to the growth medium the first two enzymes are repressed while the level of the third one increases. These data indicate that the two diverging pathways of homocysteine metabolism are anti-coordinately regulated.     

On the specificity of caffeine effects

Summary Caffeine in 0.1% or higher concentration reversibly inhibits E. coli and yeast growth. It inhibits RNA and protein synthesis (Tables 1+3) within a few minutes after being added to the incubation medium (Fig. 2). The suggestion is made that these effects of caffeine, as well as its synergism with some mutagens, are due to its ability to costack with free purines and to form complexes with single-stranded nucleic acids.