Cladosporin, a fungal
isocoumarin derivative, strongly inhibits the uptake and thereby the incorporation of
uracil and
leucine into cells of Bacillus brevis and the incorporation of
uridine but not
leucine into cells of the ascitic form of Ehrlich
carcinoma (ECA) of mice. Normal uptake was not restored by removal of the
antibiotic. In cells of Escherichia coli
A 19-15 (met-) the inhibition of
methionine uptake is associated with the cessation of growth. In a
methionine-prototrophic revertant from this organism, the uptake of
methionine is still inhibited; growth, however, is hardly affected by
cladosporin. In vitro no effect on the
DNA-dependent
RNA polymerase from E. coli and on the
RNA polymerase II from wheat germ could be detected. The
poly(U)-directed poly(Phe) synthesis was also not inhibited by
cladosporin. It is concluded that
cladosporin inhibits uptake processes which, for the case of essential nutrients, leads to loss of viability.