P-II signal transduction proteins, pivotal players in microbial nitrogen control

The P-11 family of signal transduction proteins are among the most widely d istributed signal proteins in the bacterial world. First identified in 1969 as a component of the glutamine synthetase regulatory apparatus, P-11 prot eins have since been recognized as playing a pivotal role in control of pro karyotic nitrogen metabolism. More recently, members of the family have bee n found in higher plants, where they also potentially play a role in nitrog en control. The P-11 proteins can function in the regulation of both gene t ranscription, by modulating the activity of regulatory proteins, and the ca talytic activity of enzymes involved in nitrogen metabolism. There is also emerging evidence that they may regulate the activity of proteins required for transport of nitrogen compounds into the cell. In this review we discus s the history of the P-11 proteins, their structures and biochemistry, and their distribution and functions in prokaryotes. We survey data emerging fr om bacterial genome sequences and consider other likely or potential target s for control by P-11 proteins.