The spv locus is composed of a regulatory gene , spvR , coding for a LysR-like transcription activator that positively regulates both its own gene and the spvABCD operon of structural genes ( Fang et al. 1991 , 1992 ; Krause et al. 1992 ; Guiney et al. 1995 ; Pullinger et al. 1989 ; Sheehan & Dorman 1998 ) .