The Csps and Caps that have been identified in E. coli and their putative role in
cell functions would appear from the list that the proteins are of diverse type and
involved in diverse cellular functions. Among them, the CspA family of proteins
constitute the most common type of “cold shock” proteins in bacterial species. They
are small acidic proteins with molecular mass ~7.0 kDa (Polissi et al. 2003). The
regulation of cspA gene induction after cold shock is rather complicated and as yet
not fully understood. The cspA gene shows an unusually long leader sequence. The
major transcription starts +1 is located 159 bp upstream from the translational
starting point. The promoter seems to be σ-70 dependent, since the À35 region
(TTGCAT) and the À10 region (CTTAAT) are similar to an σ-70 consensus
sequence (TTGACA) for the À35 and TATAAT for the À10 (Qoronfleh et al.
1992; Tanabe et al. 1992). There are other regulatory elements in the gene-sequence
of CspA, like the cold box (Fang et al. 1998). The 5
0 end of the Csp A m-RNA
contains a regulatory sequence (cold box), which may be responsible for cold shock
induction. The consensus sequence (5
0 UGACGUACAGA) is found in CspA,
Csp B, and Csd A. However, if the 5
0 -end of CspA containing this cold box is
overproduced, the expression of cold shock genes is no longer transient, and the
synthesis of bulk protein is impaired. Also, the cessation of regrowth after cold shock
is prolonged. This fits nicely with the observation that CspA m-RNA in excess is
poisonous to the cell. Since overproduction of CspA together with that of the 5
0 -end
restores normal cold shock response, it is likely that CspA itself interacts with the
cold box (Jiang et al. 1997). Moreover, besides CspA-mediated autoregulation, a
repressor for CspA was found to be CspE, which is abundantly produced at 37
C,
and in a CspE mutant, it is derepressed (Fang et al. 1998; Feng et al. 2001). In vitro
CspE and CspA cause transcriptional pausing just behind the cold box of CspA, and
CspA production is inhibited by addition of CspE to the translating ribosomes (Bae
et al. 1999). The induction of CspA is at least partly due to an increase in m-RNA
stability. Its half-life is 12 s at 37
C but between 15 and 30 min at 15
C (Tanabe et al.
1992). If the coding region of CspA is fused to the constitutive promoter lpp, it is still
cold inducible. This observation is explained by a strong vulnerability of the
transcript to RNase E degradation at 37
C. Even if CspA promoter is turned on
constitutively, CspA can only be synthesized if the transcript is stabilized, perhaps
by CspE (Feng et al. 2001). The transcripts CspB and CspC of Bacillus subtilis are
also dramatically stabilized, with a half-life of one minute at 37
C and more than
30 min at 15
C (Kaan et al. 1999).
Some metabolic genes are also known to influence gene expression in cold
tolerant bacteria. The PP4695 (cbrA) and PP4696 (cbrB) genes encode the sensory
box histidine kinase and a response regulator, respectively. The very similar
orthologs of this two-component system in Pseudomonas aeruginosa designated
cbrA and B were found to control utilization of carbon and nitrogen sources
(Nishijyo et al. 2001). Mutants of Pseudomonas aeruginosa deficient in cbrA and
B grew poorly on carbon sources glucose, citrate, or pyruvate and were unable to
utilize several amino acids and polyamines (Nishijyo et al. 2001). The latter
compounds play an important role in enhancing the translational efficiency (Delcher
et al. 2002) and ribosome assembly (Kakegawa et al. 1986). Considering the
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P. K. Mishra et al.
cell functions would appear from the list that the proteins are of diverse type and
involved in diverse cellular functions. Among them, the CspA family of proteins
constitute the most common type of “cold shock” proteins in bacterial species. They
are small acidic proteins with molecular mass ~7.0 kDa (Polissi et al. 2003). The
regulation of cspA gene induction after cold shock is rather complicated and as yet
not fully understood. The cspA gene shows an unusually long leader sequence. The
major transcription starts +1 is located 159 bp upstream from the translational
starting point. The promoter seems to be σ-70 dependent, since the À35 region
(TTGCAT) and the À10 region (CTTAAT) are similar to an σ-70 consensus
sequence (TTGACA) for the À35 and TATAAT for the À10 (Qoronfleh et al.
1992; Tanabe et al. 1992). There are other regulatory elements in the gene-sequence
of CspA, like the cold box (Fang et al. 1998). The 5
0 end of the Csp A m-RNA
contains a regulatory sequence (cold box), which may be responsible for cold shock
induction. The consensus sequence (5
0 UGACGUACAGA) is found in CspA,
Csp B, and Csd A. However, if the 5
0 -end of CspA containing this cold box is
overproduced, the expression of cold shock genes is no longer transient, and the
synthesis of bulk protein is impaired. Also, the cessation of regrowth after cold shock
is prolonged. This fits nicely with the observation that CspA m-RNA in excess is
poisonous to the cell. Since overproduction of CspA together with that of the 5
0 -end
restores normal cold shock response, it is likely that CspA itself interacts with the
cold box (Jiang et al. 1997). Moreover, besides CspA-mediated autoregulation, a
repressor for CspA was found to be CspE, which is abundantly produced at 37
C,
and in a CspE mutant, it is derepressed (Fang et al. 1998; Feng et al. 2001). In vitro
CspE and CspA cause transcriptional pausing just behind the cold box of CspA, and
CspA production is inhibited by addition of CspE to the translating ribosomes (Bae
et al. 1999). The induction of CspA is at least partly due to an increase in m-RNA
stability. Its half-life is 12 s at 37
C but between 15 and 30 min at 15
C (Tanabe et al.
1992). If the coding region of CspA is fused to the constitutive promoter lpp, it is still
cold inducible. This observation is explained by a strong vulnerability of the
transcript to RNase E degradation at 37
C. Even if CspA promoter is turned on
constitutively, CspA can only be synthesized if the transcript is stabilized, perhaps
by CspE (Feng et al. 2001). The transcripts CspB and CspC of Bacillus subtilis are
also dramatically stabilized, with a half-life of one minute at 37
C and more than
30 min at 15
C (Kaan et al. 1999).
Some metabolic genes are also known to influence gene expression in cold
tolerant bacteria. The PP4695 (cbrA) and PP4696 (cbrB) genes encode the sensory
box histidine kinase and a response regulator, respectively. The very similar
orthologs of this two-component system in Pseudomonas aeruginosa designated
cbrA and B were found to control utilization of carbon and nitrogen sources
(Nishijyo et al. 2001). Mutants of Pseudomonas aeruginosa deficient in cbrA and
B grew poorly on carbon sources glucose, citrate, or pyruvate and were unable to
utilize several amino acids and polyamines (Nishijyo et al. 2001). The latter
compounds play an important role in enhancing the translational efficiency (Delcher
et al. 2002) and ribosome assembly (Kakegawa et al. 1986). Considering the
202
P. K. Mishra et al.