GE 23077 factors A1, A2, B1 and B2 are novel antibiotics isolated from fermentation broths of an Actinomadura sp. strain. GE23077 antibiotics are cyclic peptides, which inhibit Escherichia coli RNA polymerase at nM concentrations. Both rifampicin-sensitive and rifampicin-resistant polymerases are inhibited, whereas E. coli DNA polymerase and wheat germ RNA polymerase are substantially not affected. In spite of the potent activity on the enzyme, the antibiotics generally show poor activity against whole cell bacteria. The spectrum of activity is restricted to Moraxella catarrhalis, including clinical isolates, with partial activity against Neisseria gonorrhoeae and Mycobacterium smegmatis.

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During the course of a screening programfor inhibitors of myo-inositol monophosphatasewe fermentedthe strain ATCC 20928, a knownproducer of L-671,776. Wenowshowthat this strain produces a complex of at least three sesquiterpenic compounds, L-671,776 (termed factor B) and two structurally related substances, termed factors A and C. Both factors A and C, like L-671,776, exhibited inhibitory activity against rayoinositol monophosphatase. Six other fungi producing the above mentioned compoundswere also isolated and taxonomically characterized.

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