Analysis of the HD and ACT domains of the E. coli signal-transducing Uridylyltransferase /Uridylyl-removing enzyme (UTase/UR)

Abstract

The uridylyl-transferase/uridylyl-removing (UTase/UR) enzyme is part of two important signaling cascade mechanisms that control cellular function in response to signals of carbon and nitrogen status (figure 1). The sequence of UTase/UR, from the gln D gene located on the glnALG operon in E. coli, encodes three domains that are highly conserved across a number of other proteins, namely the NT, HD, and ACT domains. The NT (nucleotidyltransferase) domain has been studied in great depth. However, little is known about the HD and ACT domains. One specific mutation, D105N, has been found to cause the loss of both activities of UTase/UR. In response, it has been suggested that the two catalytic activities of UTase/UR are located within the NT domain. In this experiment, mutations of highly conserved residues in the HD and ACT domains of UTase/UR were studied to determine effects on enzyme wild-type function. Understanding how these domains contribute to proper enzyme function in UTase/UR can offer insight about their role in other proteins in which they are present.