CspB and CspL, thermostable cold-shock proteins from Thermotoga maritima

Cold-shock proteins (Csps) are important for cellular adaptation to low temperature. Csps help cells adapt to low-temperature growth through their RNA-binding and nucleic acid melting abilities, which lead to anti-termination of transcription.

We studied the two most thermostable Csps known to date, TmCspB and TmCspL from Thermotoga maritima, a hyperthermophilic eubacterium for which no cold-shock response has been demonstrated so far. For comparison, we used a well-characterized Escherichia coli CspE protein. TmCspB and TmCspL are able to bind RNA at both low and high temperatures. They are also able to 'melt' nucleic acids secondary structures and as a result decrease E. coli RNA polymerase transcription termination in vivo and E. coli and T. maritima RNA polymerases transcription termination in vitro. Over-expression of TmCsps allowed E. coli cold-sensitive mutant cells to acclimate to the low temperatures of 15 degrees C.

TmCspB and TmCspL (i) are able to perform essential functions of E. coli Csps in vitro and in vivo, 50-65 degrees C below the temperature optimum of T. maritima and (ii) can anti-terminate transcription by T. maritima RNA polymerase at 55 degrees C, the lower limit of temperature range for growth of T. maritima. We propose that the observed properties of TmCsps are physiologically relevant and that TmCsps are important for adaptation of T. maritima to physiologically low temperatures.