EFFECTS OF UPSTREAM DELETIONS ON LIGHT-REGULATED AND OXYGEN-REGULATED BACTERIOOPSIN GENE-EXPRESSION IN HALOBACTERIUM-HALOBIUM

The bacterio-opsin gene (hop) of Halobacterium halobium is located within a cluster with three other genes. Growth conditions of high light intensity and low oxygen tension induce hop gene cluster expression. To identify putative regulatory factor binding sites upstream of the hop gene, we have compared sequences upstream of the hop gene with the corresponding sequences from two other genes in the hop gene cluster. Conserved sequence motifs were observed which may mediate the effect of high light intensity and/or low oxygen tension on hop gene expression. Based on these motifs, a set of mutants was constructed which contained deletions upstream of the hop gene. These constructs were tested in a host strain where hop gene expression is independent of oxygen regulation and in another strain where it is regulated by oxygen and light. The minimal upstream sequence required for both light- and oxygen-regulated hop gene expression was determined to be 54 bp.