Control of Gene Action in Phage SPO1 Development: Phage-specific Modifications of RNA Polymerase and a Mechanism of Positive Regulation

Abstract

INTRODUCTION
Phage SPO1 is a member of a group of closely related DNA phages of Bacillus subtilis. These large, tailed phages contain double-stranded DNA (molecular weight ca. 10⁸) in which hydroxymethyluracil (hmU) replaces thymine. The phages are lytic, yet they establish host–virus metabolic relationships that differ from those of the phages of Escherichia coli, particularly with respect to host genome degradation, shutoff of host cell macromolecular synthesis and the existence of cellular carrier states for these viruses (Shub 1966; Pène 1968; Gage 1969; Yehle and Ganesan 1972; Cocito 1974).

Program of Viral Gene Expression during Phage SPO1 Development
The development cycle of these phages is marked by a relatively clearly defined pattern of gene expression that can be discerned by examining the synthesis of viral proteins or RNA (Shub 1966; Levinthal, Hosoda and Shub 1967; Gage and Geiduschek 1967,1971a,b). SPO1 mRNA, unlike T7 mRNA, is chemically unstable.¹ Accordingly, the concentration of a group of messages decreases as soon as they cease to be synthesized, and one can therefore follow the synthesis and degradation of different groups of messages quite closely by hybridization-competition analysis. Six groups of SPO1 messages can be distinguished on the basis of their times of first appearance and cessation of synthesis. If any collection of SPO1 transcripts is made throughout viral development, they must constitute a small part of viral transcription both at the beginning and at the end of viral development (Gage and Geiduschek 1971a,b). It is useful to distinguish roughly early, middle and late...