Analysis of early promoters of the Bacillus bacteriophage GA-1

Bacteriophage GA-1, which infects Bacillus sp. strain G1R, is evolutionaril y related to phage phi 29, which infects Bacillus subtilis. We report the c haracterization of several GA-1 promoters located at either end of its line ar genome. Some of them are unique for GA-1 and drive the expression of ope n reading frames that have no counterparts in the genome of phi 29 or relat ed phages. These unique promoters are active at early infection times and a re repressed at late times. In vitro transcription reactions revealed that the purified GA-1-encoded protein p6 represses the activity of these promot ers, although the amount of p6 required to repress transcription was differ ent for each promoter. The level of protein p6 produced in vivo increases r apidly during the first stage of the infection cycle. The protein p6 concen tration may serve to modulate the expression of these early promoters as in fection proceeds.