Practice question

Cold shock from abrupt downshift to 10 to 20 degrees stabilizes mRNA secondary structures such as hairpins and pseudoknots in the 5 prime untranslated region, blocking 30S ribosome binding and causing premature transcription termination. Bacteria produce abundant small cold shock proteins CspA to CspI, members of 7 kDa single-stranded nucleic acid binding family with conserved cold-shock domain containing RNP motifs binding RNA cooperatively. These act as RNA chaperones destabilizing inhibitory structures, melting hairpins and exposing Shine-Dalgarno ribosome binding site as accessible single strand, thus specifically enhancing translation initiation of essential housekeeping genes required during cold adaptation. CspA also functions as transcription antiterminator increasing readthrough of Rho-dependent terminators and autoregulates its own mRNA stability via feedback. It does not degrade mRNA indiscriminately nor increase membrane rigidity nor inhibit DNA replication; rather it preserves membrane fluidity indirectly via induction of fatty acid desaturases introducing unsaturated bonds and restores active protein synthesis permitting resumed growth after cold exposure, crucial for psychrotrophic survival.