Psi factor is a substance produced by Aspergillus nidulans that induces premature sexual sporulation. Chromatographic analysis of psi-active extracts showed that psi activity resides in several different forms. Two of the forms, psiAl and psiBl, have been isolated and have been shown to have closely similar compositions. The most abundant form, psiAl, reacts with alcohols in acidic solution by the addition of one entire molecule of the alcohol. This reaction, which is reversible, suggests that psiAl may be a lactone whose ring is opened by alcohol addition. At high concentration, psiAl is antagonistic to the response exhibited by the other forms of psi, but this antagonism is lost by the alcoholic derivatives. At least one unpurified psi species can be converted to psiAl by acid catalysis. We suggest that psiAl may be the metabolic precursor of at least some of the other more active psi components and that this conversion during Aspergillus development may be part of the process that triggers sexual sporulation.Fungi propagate principally by the formation of spores which can be either asexual or sexual. Asexual spores (conidia) are produced by mitosis of haploid nuclei, whereas sexual spores are generated by meiosis of diploid nuclei. The two haploid components of the diploid nuclei may be derived from the same strain (homothallic species) or may be obligatorily derived from different strains (heterothallic species) which are said to be of opposite mating type. Many species, including homothallic Aspergillus nidulans, exhibit both asexual and sexual sporulation.When initiated from spores, fungal colonies usually grow at first by extension of their hyphal filaments (vegetative growth) and at some later time abruptly begin to make spores, either asexual, sexual, or both. The switch from vegetative growth to sporulation is accompanied by the activation of a large number of genes which can account for a considerable fraction of the expressed fungal genome. In A. nidulans, over 1,000 new mRNA species appear during asexual sporulation (8). A fundamental question is the nature of the signal that initiates sporulation and how this signal is transduced to the level of the gene.In some fungal species, sexual sporulation has been shown to be mediated by specific metabolites that are secreted in very small amounts and which can reasonably be termed hormones. In the few cases for which the active agents have been characterized (4), they are terpenoids (the trisporic acids of Mucor species), steroids (antheridiol and oogoniols of Achlya species), or peptides (a and a factors of Saccharomyces cerevisiae).Confluent plate cultures of A. nidulans normally develop in a well-defined sequence in which asexual sporulation precedes sexual sporulation. We have previously demonstrated that this organism produces a substance with potent hormonelike activity, called psi factor, that induces premature sexual sporulation, causing the two sporulation modes to overlap (3). Active extracts also cause an attenuation of asexual sporulation, whic...
During development of the homothallic ascomycete Aspergillus nidulans, asexual sporulation is followed by sexual sporulation. We report here the detection of a solvent-extractable activity which inhibits asexual sporulation and stimulates premature sexual sporulation. This activity, called precocious sexual inducer (psi), is overproduced by certain mutants that are blocked in both modes of sporulation. Using partially purified preparations of psi, biological response could be elicited with as little as 50 ng of material. We suggest that psi is a hormone-precursor which is converted to a hormone by normal sporulating strains that respond to psi, but not by the asporogenous mutants that overproduce psi. The stability of psi activity gives promise that the compound can be purified and identified. I N T R O D U C T I O NThe filamentous fungus Aspergillus nidulans has been the subject of extensive genetic and biochemical research over the past forty years. It is also an attractive organism for developmental studies because it exhibits a simple and highly regulated programme of cell differentiation. The developmental stages of a confluent agar surface culture originated from dormant spores are shown in Fig. 1. After spore germination and a period of undifferentiated vegetative growth, mitotically-generated asexual spores (conidia) suddenly appear in great numbers and become dark green. As this burst of conidiation ceases, sexual development commences with the formation of cleistothecia. These small spherical shells, -200 pm in diameter, are the sexual fruiting bodies in which bright-red ascospores are later generated by meiosis. The onset of conidiation is accompanied by the appearance of over 1000 mRNA species not found in vegetative hyphae (Timberlake, 1980). In previous reports (Butnick et al., 1984a, b) we described the properties of three unusual thermosensitive asporogenous mutants which, although non-allelic, exhibited the same biochemical abnormality. At the restrictive temperature (42 "C) each secreted a set of solventextractable metabolites into the culture medium at levels much higher than the parental strain or other asporogenous mutants. One of the major components has been identified as diorcinol(3,3'-dihydroxy-$5'-dimethyldiphenyl ether), the origin of which is probably the polyketide precursor orsellinic acid (Ballantine et al., 1971). Preliminary analyses of several of the other components indicate similar phenolic compounds. Mutants which exhibit this phenotype we call phenolic over producing (POP) mutants and we refer to the overproduced compounds as the POP metabolites. That a single mutation results in the appearance of a variety of compounds suggests that these compounds are accumulated intermediates or shunt products of some metabolic pathway which is blocked by the mutation. Although isolated for their inability to form conidia, and given the gene symbol aco, all three POP mutants were found to be blocked in sexual sporulation as well. This report describes the detection of a hormone-like facto...
The structures of four hydroxylated unsaturated CI8 fatty acids (psi factors) which induce premature sexual sporulation in A, nidulans, and the enantioselective synthesis of two of the components, psiBa and psiB(3, are described.We have reported the characterization of endogenous factors, psiAa 1 and psiAfi 2, which induce premature sexual sporulation in the ascomycetous fungus Aspergillus nidulans.132 The characterization? of psiBa 3a, psiB(3 4a, psiCa Sa, and psiCfi 6a, with higher sporogenic activity, and the synthesis of psiBa 3a and psiB(3 4a are described below.Crude psiB and psiC, IR Y 1710cm-1 (COzH), were esterified with diazomethane and purified by HPLC (CIS, 80% MeCN-H20) to yield the methyl esters psiBa 3b, psiB(3 4b, psi& Sb, and psiC(3 6b. Analysis of spectroscopic data of 3b indicated that acid 3a is identical with laetisaric acid (8-OH configuration undetermined), an allelopathic agent produced by the basidiomycete fungus Laetisaria arvaZis.3 The 1H and 13C NMR of psiB(3 methyl ester 4b showed the presence of secondary O H and a cis-disubstituted double bond ( J g , l o = 11 .O Hz). Location of 8-OH in the psiB's was confirmed by the mass spectrum of the perhydro trimethylsilyl ether derivative 7, which showed peaks corresponding to cleavage at C-7-C-8 (mlz 243, C14H310Si) and C-8-C-9 (rnlz 245, C12H2503Si); the absolute configuration was established as (8R) from the CD4 of the p-bromobenzoate of psiB(3 methyl ester 4c, hext(A&) 243 nm (-7.5) in MeCN. The structures of psiBa and psiB(3 are thus (8R)-(Z, Z)-hydroxyoctadeca-9,12-dienoic acid and (8R)-(Z)-hydroxyoactadec-9-enoic acid, respectively.PsiCs are readily converted to psiAs, particularly with acid, the products being identified with authentic psiAs by TLC and HPLC; furthermore, the conversion products yield psiC
gestive that conformational preference is the factor responsible for the magnetic nonequivalence of the methylene protons of IV.Further support for this conclusion is provided by the n.m.r. spectrum of the substituted cyclobutenone VI (Fig. 2). The resonance centered on 113 cps is of the methylene protons of the ethyl group of this compound and is the rather complicated AB part of an ABC3X system. The resonance of the methine proton at the 4-position of the cyclobutene ring is centered on 233 cps and is split into two equally intense doublets, rather than a 1:2:1 triplet. This splitting is most simply explained as the result of unequal coupling between the methine proton and the two adjacent methylene protons, arising from a preference for a conformation for the molecule in which the methine proton is trans to one methylene proton and gauche to the other.For the genetic information in a cistron to be translated into a polypeptide chain' each coding unit in the nucleotide sequence must correspond to one of the twenty or so amino acids. If not every possible sequence corresponds to an amino acid, mutations that substitute one base for another could, in certain cases, cause the continuity of the information to be interrupted, and such-"nonsense" mutations would block completion of the polypeptide chain.By virtue of a mutant with special properties, it is possible to identify nonsense mutations within the A cistron of the rII region of phage T4. In this paper the criterion for nonsense is applied to certain "ambivalent" rII mutants,' i.e., ones whose phenotypes can be reversed by suppressor mutations in the bacterial host, Escherichia coli. The results show that an ambivalent mutation that behaves like nonsense in one bacterial host may nevertheless make sense in a second (suppressor containing) host. This suggests that a suppressor mutation in the bacterium can result in addition to the cell's dictionary of a new sensible coding unit, constituting a change in the genetic code of the bacterial cell.The r1589 System as a Genetic Test for Nonsense Mutations.-The rnl genetic region of phage T4 consists of two contiguous regions, A and B, each behaving as a
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