Identification of a functional CT-element in the Phytophthora infestans piypt1 gene promoter

CT-rich sequences of incompletely characterized function have been found in the gene promoter regions of many organisms, fungi and members of the genus Phytophthora prominently among them. We describe here an in vitro analysis of CT-element function in regulating transcription of the Phytophthora infestans piypt1 gene, a gene that encodes a monomeric G-protein believed to be involved in regulation of vesicle transport (Chen and Roxby (1996) Gene 181, 89-94). The results of the promoter analysis indicate that a 17-bp CT-element lying close to the transcription start point of this gene is important in determining the frequency of transcription initiation. Competition experiments suggest that transcription factors bind to the CT element. A subregion lying at the 5'-end of the CT-element resembles an Inr element, a type of CT-rich transcription regulator first discovered in some mammalian genes. This Inr-like subregion appears to be more important in the interactions leading to transcription initiation than more downstream regions within this CT-element. Two proteins, of 37 and 45 kDa, respectively, that bind to the CT-element and are presumed to be transcription factors were detected in P. infestans nuclear extracts by southwestern blotting.