The initial observation in P. £uorescens ST that the ‘sty’
genes were clustered on the chromosome raised the possibility
that a pathway-speci¢c regulatory apparatus could
also be in close proximity. This was indeed established by
Velasco et al. following complementation studies in E. coli
Wwith elements of the Pseudomonas sp. strain Y2 sty
operon [15]. It was reported that expression of the catabolic
operon in E. coli Wwas signi¢cantly reduced in the
absence of two genes, styS and styR, located upstream
from the styrene catabolic operon. Expression was restored
when these genes were provided in trans. Several
studies have since reinforced the essential function of
stySR in styrene catabolism and their role in pathway
regulation will be dealt with in more detail below. styS
and styR (Table 1; Fig. 2) encode two proteins which
display a high level of amino acid similarity with members
of the superfamily of two-component signal transduction
systems found in both prokaryotes and eukaryotes [27,32].
Based on sequence analysis and RT-PCR investigations, it
appears that both genes are expressed in a transcriptionally
coupled fashion [19].