Aerobic and anaerobic regulation in XXXX : the role of the @entity60180 gene.

@entity1568 @entity26 @entity72005 @entity72006 @entity60180 @entity3733 @entity2518 @entity31599 @entity19062 @entity16258
In @entity31599 , the cellular requirements for @entity2518 (ALA) are in part regulated by the level of ALA synthase activity, which is encoded by the @entity72005 and @entity72006 genes. Under standard growth conditions, only the @entity72005 gene is transcribed, and the level of ALA synthase activity varies in response to @entity26 tension. The presence of an FNR consensus sequence upstream of @entity72005 suggested that @entity26 regulation of @entity72005 expression could be mediated, in part, through a homolog of the fnr gene. Two independent studies, one detailed here, identified a region of the @entity31599 genome containing extensive homology to the fix region of the symbiotic @entity1568 -fixing bacteria @entity16258 and @entity19062 . Within this region that maps to 443 kbp on chromsome I, we have identified an fnr homolog ( @entity60180 ), as well as a gene that codes for an anaerobic coproporphyrinogen III oxidase, the second such gene identified in this organism. We also present an analysis of the role of @entity60180 in the physiology of @entity31599 through the construction and characterization of @entity60180 -null strains. Our results further show that @entity60180 is essential for both photosynthetic and anaerobic-dark growth with @entity3733 . Analysis of @entity72005 expression, with @entity72005 ::lacZ transcriptional fusions, suggests that @entity60180 is an activator of @entity72005 under anaerobic conditions. On the other hand, the open reading frame immediately upstream of @entity72005 appears to be an activator of @entity72005 transcription regardless of either the presence or the absence of @entity26 or @entity60180 . Given the lack of @entity72006 expression under these conditions, we consider @entity60180 regulation of @entity72005 expression to be a major factor in bringing about changes in the level of ALA synthase activity in response to changes in @entity26 tension.
