Browsing by Subject "Inositol"

Inositol phosphates (IPs) are eukaryotic signaling molecules that play important roles in a wide range of biological processes. IPs are required for embryonic development and patterning, insulin secretion, the regulation of telomere length, proper progression through the cell cycle, and the regulation of ion channels. This work uses the yeast Saccharomyces cerevisiae as a model system for investigating the functions of IPs and focuses on the transcriptional regulation of the gene encoding the secreted mating pheromone MFα2 by the IP kinase Ipk2 (also called Arg82, ArgR3, and IPMK). This work shows that Ipk2 has both kinase-dependent and kinase-independent functions in regulating the transcription of MFα2. Transcription of MFα2 is also dependent upon the integrity of an Mcm1-binding site in its promoter. This is the first description of a role for this binding site in the transcription of MFα2.

In vivo and in vitro screening approaches to identify additional factors associated with MFα2 expression or with IP biology generally are also described. These unbiased approaches provide some valuable insight for further investigations.

Inositol Polyphosphate Multi-Kinase (IPMK, also known as ArgRIII, Arg82, and IPK2) is a central component of the inositol signaling system, catalyzing the phosphorylation of at least four different inositol polyphosphate species in vivo with in vitro activity observed for three more. Each of these IP species is sterically unique and the phosphorylation target varies between the 6'-, 3'-, or 5'-hydroxyls, classifying IPMK as a 6/3/5-kinase. The products of IPMK have been linked to multiple processes including cell cycle regulation, transcriptional control, telomere length regulation, mRNA export and various phenotypes including mouse embryonic and fly larvae development, and stress responses in plants and yeast. Linking specific IP species and cellular processes has been complicated by the inability to distinguish between the different effects of the various IP species generated by IPMK. Deletion of IPMK affects the IP populations of all its various substrates and products and therefore the role of a single IP species cannot be tracked. The goals of this work were to address the question of substrate selectivity and develop new tools to probe inositol signaling in vivo through a combination of structural, enzymatic, and genomic techniques.

The structure of Arabidopsis thaliana IPMK is reported at 2.9Å resolution and in conjunction with a new model of inositol selectivity has been used to design constructs with altered substrate profiles. In vitro and in vivo experiments have confirmed that IPMK identifies substrate inositol polyphosphate species through a recognition surface that requires phosphate groups occupy specific pockets and rejects those with axial phosphate groups in specific regions. In vivo experiments have linked specific inositol polyphosphate species to nitrogen metabolism and temperature sensitivity in yeast and established the potential for these constructs to be used to probe signaling in other organisms.