Pop2: A Potential Regulator of Hmt1-Catalyzed Arginine Methylation in Yeast

Document Type

Presentation

Publication Date

4-10-2014

Faculty Mentor

Joan Hevel

Abstract

Protein Arginine methylation is an important post-translational modification that is vital in regulating various cellular processes such as gene transcription, cell signaling, and RNA processing. Protein arginine methyltransferases (PRMTs) are responsible for performing this important modification. PRMT1 (protein arginine methyltransferase 1) and Hmt1 (hnRNP methyltransferase 1) are the predominant PRMTs in humans and yeast, respectively. Despite growing momentum in this field, relatively little is understood about PRMT regulation. Further work discovering how PRMTs are regulated will greatly advance our understanding of diseases where PRMTs have been implicated, such as heart disease and cancer. It has been discovered that a human protein called hCaf1 (human Ccr4-associated factor 1) is a regulator of PRMT1 with respect to certain substrates, and also colocalizes with PRMT1. We present data that suggest the yeast homolog of hCaf1, Pop2, may also perform a similar function on Hmt1. We provide data on the expression and purification of a truncation of Pop2 from S. cerevisiae, including the temperature sensitivity of one construct of Pop2 and its susceptibility to precipitation. We also demonstrated concentration-dependent inhibition of Hmt1-catalyzed methylation of histone H4 by Pop2 in vitro. Yeast cell lysates also showed altered patterns of methylation in the presence and absence of Pop2 in vivo. In an effort to understand the mechanism employed by Pop2 to accomplish this regulatory function, pull-downs were performed suggesting that Pop2 directly interacts with histone H4, a substrate of Hmt1. Mutagenic studies with Pop2 suggested a region that may be responsible for this interaction. Given these data, we hypothesized that Pop2 is able to inhibit the methylation of histone H4 via a substrate-sequestering mechanism. Further experimentation will determine the precise interaction surfaces of Pop2 and substrate, and continue to define the details of methylation inhibition by Pop2, including the scope of its influence in the cell.

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