TRANSCRIPTIONAL REGULATION OF PUC OPERON EXPRESSION IN RHODOBACTER-SPHAEROIDES - INVOLVEMENT OF AN INTEGRATION HOST FACTOR-BINDING SEQUENCE

The putative overlapping consensus sequences (-129 to -105) for bindin g of fumarate nitrate reductase regulator- and integration host factor (IHF)-like proteins to puc operon upstream DNA of Rhodobacter sphaero ides was protected from DNase I digestion by purified Escherichia coli IHF. The binding of E. coli IHF to the purported IHF-binding site in the puc upstream DNA is highly sequence-specific. The recorded binding affinity was significantly lower than that of E. coli IHF to the lamb da attP site. Employing site-directed changes in the DNA sequence with in the -129 to -105 region, a loss in IHF binding, as monitored throug h gel retardation analysis, was correlated with alterations in puc ope ron expression monitored through the use of puc=lacZ transcriptional f usions. These results suggest that the IHF-binding site is involved in repression of puc operon transcription by oxygen as well as modulatio n of puc operon transcription levels by incident light intensity. Muta tions specific to the upstream half of the putative fumarate nitrate r eductase regulator-binding site of the puc upstream DNA did not show a ny physiological effects under the experimental conditions employed. T aken together, these studies reveal that the DNA sequence between -129 to -105 may involve facilitation of the interaction between upstream and downstream cis-acting regulatory sequences involved in puc operon expression.