Selective expression of the β‐subunit of nucleoid‐associated protein HU during cold shock in Escherichia coli

Abstract

Expression of Escherichia coli hupA and hupB, the structural genes encoding the most abundant nucleoid-associated proteins HUα and HUβ has been studied during cold shock. This article demonstrates that: (i) transcriptional expression of hupA is blocked following a sudden temperature downshift (from 37°C to 10°C), whereas transcription of hupB from the P2 and P3 promoters is maintained at a constitutive level and is activated de novo from the P4 promoter; (ii) all three hupB mRNAs (transcribed from the three natural promoters P2, P3 and P4) become much more stable than the single hupA transcript; and (iii) the hupB transcripts, unlike that of hupA, are efficiently translated in vivo during cold acclimation and can be actively translated in vitro at low temperature. Taken together, the results indicate that during cold shock the expression of the HUβ subunit is preferentially stimulated and that of HUα repressed, suggesting that an altered HUα to HUβ expression ratio resulting in an increase of HUα/HUβ heterodimers and/or (HUβ)₂ homodimers may play an important role during cold adaptation.