15 Antitermination and the Control of Transcription Elongation

Abstract

OVERVIEW
Certain regulatory proteins determine how far RNA polymerase goes rather than where it starts. Their defining property is the ability to recognize a specific site in a transcription unit and to modify RNA polymerase near this site, changing its properties so that RNA chains are elongated more efficiently. Usually this means that RNA polymerase goes through sites that for unmodified RNA polymerase are terminators (antitermination), so that genes downstream from a terminator are expressed. However, such modification also might affect the rate or time of gene expression simply by altering the overall rate of elongation, or the time that RNA polymerase pauses at certain sites. We do not discuss attenuation (see Landick and Turnbough, this volume) or regulation by factors like the Escherichia coli Bgl protein (Houman et al. 1990), because these mechanisms involve modifications of specific terminators rather than alterations of RNA polymerase.

INTRODUCTION AND PERSPECTIVE
Antitermination through modification of RNA polymerase occurs in at least three E. coli regulatory systems. Two of these are made by the E. coli bacteriophage λ, whose genes N and Q encode antiterminators that control phage early and late gene products, respectively (for review, see Friedman and Gottesman 1983; Friedman 1988; Roberts 1988). A mechanism perhaps closely related to that of λ N protein controls elongation of transcription of the E. coli ribosomal RNA operons (Morgan 1980; Li et al. 1984; Albrechtsen et al. 1990), although, in contrast to the operons controlled by N and Q, no specific terminators have been found...