Genetics - Theses

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    Molecular studies of gene regulation in Aspergillus nidulans
    Atkinson, Peter William ( 1985)
    The amdA regulatory gene of Aspergillus nidulans controls the expression of both the acetamidase (amdS) gene and a gene, designated aciA, which encodes a 42 000 dalton polypeptide. The cloning and analysis of the aciA gene is described in this thesis. The aciA gene is a single copy gene approximately 2kb in size and encodes two messenger RNA species of 1.45 and 1.55kb•in size. Both of these aciA transcripts are regulated in an identical fashion. The aciA gene is demonstrated to be induced in the presence of the carbon source acetate and evidence is presented which indicates that it may also be subject to carbon catabolite repression. None of the other regulatory circuits which are known to control amdS expression affect the expression of the aciA gene. The 5' non-coding region of the aciA gene was sequenced and both the primary and secondary structures within this region are compared with the corresponding regions of the amdS gene and a cis-acting mutant of the amdS gene which increases the amdA-mediated regulation of this gene. The aciA gene possesses a canonical TATA box and also contains a number of other sequences which are similar to sequences found in the 5' non-coding region of the amdS gene. The most interesting of these is a 23bp purine-rich region which is similar to a purine-rich region occurring in approximately the same position in the amdS gene. This sequence is found to be duplicated in the amdS mutant which is subject to increased regulation by the amdA gene. Experiments in which A. nidulans was transformed with multicopy plasmids containing DNA fragments from the aciA gene have indicated that the aciA sequence responsible for the titration of the amdA gene product is located in the 5' non-coding region of this gene. A model for the regulation of the aciA gene by the amdA gene, acetate and carbon catabolite repression is presented. The possible significance of small repeated sequences within the purine-rich regions of aciA and amdS is also discussed.