AbrB, a Transition State Regulator

Abstract

Studies of isolated ribosomes from Spo0 versus Spo0 abrB mutants indicated that abrB led to alterations or deficiencies in one or more ribosomal proteins. The first three residues of the predicted protein are Met-Phe-Met, but another study of the AbrB protein produced from an expression vector in Escherichia coli revealed that the amino terminus of the purified protein begins at the second methionine residue. Although AbrB appears to play three different roles (repressor, “preventer,” and activator), the overall purpose of AbrB-mediated regulation is to prevent the expression of postexponential-phase genes at inappropriate times, such as during vegetative growth on good nutrient sources. A physical interaction of bound AbrB with other transition state regulators may be a hallmark of the regulatory mechanism at “prevented” genes. A complete understanding of how AbrB regulates transition state gene expression requires understanding how AbrB itself is regulated. The current model of the role AbrB plays in the regulation of transition state events. Some regulate other homeotic selector genes, and some are subject to autoregulation. During vegetative growth, AbrB prevents inappropriate functions from being expressed by (i) direct repression, (ii) action in concert with other regulators (preventers), or (iii) activation of other transition state repressors-preventers (such as Hpr).