Nucleotide sequence and functional analysis of cbbR, a positive regulator of the Calvin cycle operons of Rhodobacter sphaeroides

Abstract

Structural genes encoding Calvin cycle enzymes in Rhodobacter sphaeroides are duplicated and organized within two physically distinct transcriptional units, the form I and form II cbb operons. Nucleotide sequence determination of the region upstream of the form I operon revealed a divergently transcribed open reading frame, cbbR, that showed significant similarity to the LysR family of transcriptional regulatory proteins. Mutants containing an insertionally inactivated cbbR gene were impaired in photoheterotrophic growth and completely unable to grow photolithoautotrophically with CO2 as the sole carbon source. In the cbbR strain, expression of genes within the form I operon was completely abolished and that of the form II operon was reduced to about 30% of the wild-type level. The cloned cbbR gene complemented the mutant for wild-type growth characteristics, and normal levels of ribulose 1,5-bisphosphate carboxylase/oxygenase (RubisCO) were observed. However, rocket immunoelectrophoresis revealed that the wild-type level of RubisCO was due to overexpression of the form II enzyme, whereas expression of the form I RubisCO was 10% of that of the wild-type strain. The cbbR insertional inactivation did not appear to affect aerobic expression of either CO2 fixation operon, but preliminary evidence suggests that the constitutive expression of the form II operon observed in the cbbR strain may be subject to repression during aerobic growth.

The role of two CbbRs in the transcriptional regulation of three ribulose-1,5-bisphosphate carboxylase/oxygenase genes in Hydrogenovibrio marinus strain MH-110

“…Although the cbbR genes are located upstream of genes encoding RubisCO in a divergent orientation in most bacteria, the number of cbbR genes is not equivalent to that of genes for RubisCO (Windhövel & Bowien, 1991;Gibson & Tabita, 1993;Meijer et al, 1996;Kusian & Bowien, 1997;Smith & Tabita, 2002;Dubbs & Tabita, 2003). For example, a single cbbR gene product regulates two cbb operons in Rhodobacter sphaeroides (Gibson & Tabita, 1993;Smith & Tabita, 2002;Dubbs & Tabita, 2003). In H. marinus, the cbbR genes were found upstream of cbbLS-1 and cbbM, and were designated cbbR1 and cbbRm, respectively; however, no regulatory genes were found upstream of cbbLS-2 ( Fig.…”

“…CbbR, one of the LysR-type transcriptional regulators (LTTRs), has been found in many photo-and chemoautotrophic bacteria, and has been shown to be required to activate expression of RubisCO (Windhövel & Bowien, 1991;Falcone & Tabita, 1993;Gibson & Tabita, 1993;van den Bergh et al, 1993;Paoli et al, 1998;Dubbs et al, 2000Dubbs et al, , 2004Vichivanives et al, 2000). Although the cbbR genes are located upstream of genes encoding RubisCO in a divergent orientation in most bacteria, the number of cbbR genes is not equivalent to that of genes for RubisCO (Windhövel & Bowien, 1991;Gibson & Tabita, 1993;Meijer et al, 1996;Kusian & Bowien, 1997;Smith & Tabita, 2002;Dubbs & Tabita, 2003).…”

Interactions of the cbbII Promoter-Operator Region with CbbR and RegA (PrrA) Regulators Indicate Distinct Mechanisms to Control Expression of the Two cbb Operons of Rhodobacter sphaeroides

“…Strain 1312 harbors an inactivated CbbR because of the insertion of a trimethoprim resistance cassette within the cbbR gene (12). Consequently, strain 1312 does not synthesize form I Rubisco and accumulates only low levels of form II Rubisco compared with wild-type R. sphaeroides.…”

“…In addition to the apparent independent regulation of cbb I and cbb II gene expression, a mechanism for interdependent regulation also exists that results in a compensatory increase in the expression of one operon when the other is inactivated (4,7,9,10). The cbbR gene, which encodes a LysR-type transcriptional regulator, is located immediately upstream and divergently transcribed from cbbF I (12) and mediates this compensatory effect. CbbR is a positive regulator of the expression of both the cbb I and cbb II operons (12,13).…”

“…The cbbR gene, which encodes a LysR-type transcriptional regulator, is located immediately upstream and divergently transcribed from cbbF I (12) and mediates this compensatory effect. CbbR is a positive regulator of the expression of both the cbb I and cbb II operons (12,13). The regA-regB (prrA-prrB) two component regulatory system, encoding sensor kinase RegB (PrrB) and response regulator RegA (PrrA) also plays a role in cbb regulation.…”