| Abstrakt: |
A new gene ofNeurospora crassa, designatedpco-1, was characterized and shown to regulate the expression of several genes which encode enzymes required for the catabolism of purines. Unlike the wild type, apco-1mutant created by repeat-induced point mutation cannot utilize purines as a nitrogen source. The PCO1 protein contains a Zn(II)2Cys6 binuclear cluster motif near its N-terminus, followed by a putative coiled-coil motif. A chemical crosslinking experiment demonstrated that PCO1 forms homodimers. PCO1 binds to CGG-N6-CCG elements located in the upstream promoter region of four genes encoding purine catabolic enzymes. Northern blot analysis demonstrated that a functional PCO1 protein is required for induction ofxdh, which encodes xanthine dehydrogenase. Moreover, PCO1 was required for induction of three different purine catabolic enzymes. Two glutamine-rich domains occur in the C-terminal region of PCO1 and at least one of the glutamine-rich regions is required for PCO1 function, suggesting that they might play a role in transcriptional activation. The PCO1 protein does not interact with the global-acting NIT2 protein or the negative-acting NMR protein that functions in nitrogen catabolite repression. Induction of thexdhgene and synthesis of xanthine dehydrogenase is completely dependent upon PCO1, but does not require the global-acting NIT2 protein, suggesting that it is controlled by a novel regulatory mechanism. [ABSTRACT FROM AUTHOR] |
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