AUTHOR=Zhang Bo , Yue Lei , Zhou Liguang , Qi Lei , Li Jie , Dong Xiuzhu 

TITLE=Conserved TRAM Domain Functions as an Archaeal Cold Shock Protein via RNA Chaperone Activity

JOURNAL=Frontiers in Microbiology

VOLUME=8

YEAR=2017

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2017.01597

DOI=10.3389/fmicb.2017.01597

ISSN=1664-302X

ABSTRACT=<p>Cold shock proteins (Csps) enable organisms to acclimate to and survive in cold environments and the bacterial CspA family exerts the cold protection via its RNA chaperone activity. However, most Archaea do not contain orthologs to the bacterial <italic>csp</italic>. TRAM, a conserved domain among RNA modification proteins ubiquitously distributed in organisms, occurs as an individual protein in most archaeal phyla and has a structural similarity to Csp proteins, yet its biological functions remain unknown. Through physiological and biochemical studies on four TRAM proteins from a cold adaptive archaeon <italic>Methanolobus psychrophilus</italic> R15, this work demonstrated that TRAM is an archaeal Csp and exhibits RNA chaperone activity. Three TRAM encoding genes (<italic>Mpsy_0643, Mpsy_3043</italic>, and <italic>Mpsy_3066</italic>) exhibited remarkable cold-shock induced transcription and were preferentially translated at lower temperature (18°C), while the fourth (<italic>Mpsy_2002</italic>) was constitutively expressed. They were all able to complement the <italic>cspABGE</italic> mutant of <italic>Escherichia coli</italic> BX04 that does not grow in cold temperatures and showed transcriptional antitermination. TRAM3066 (gene product of <italic>Mpsy_3066</italic>) and TRAM2002 (gene product of <italic>Mpsy_2002</italic>) displayed sequence-non-specific RNA but not DNA binding activity, and TRAM3066 assisted RNases in degradation of structured RNA, thus validating the RNA chaperone activity of TRAMs. Given the chaperone activity, TRAM is predicted to function beyond a Csp.</p>