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Transcription Antitermination by Translation Initiation Factor IF1

Department of Biochemistry, Robert Wood Johnson Medical School, 675 Hoes Lane,¹ Waksman Institute, Department of Biochemistry and Molecular Biology, Rutgers, The State University of New Jersey, 190 Frelinghuysen Road, Piscataway, New Jersey 08854,² Basic Research Program, SAIC-Frederick, Inc.,³ Molecular Control and Genetics Section, Gene Regulation and Chromosome Biology Laboratory, Center for Cancer Research, National Cancer Institute at Frederick, Frederick, Maryland 21702,⁴ Department of Microbiology and Immunology, SUNY Downstate Medical Center, Brooklyn, New York 11203⁵

Received 5 February 2007/ Accepted 13 March 2007

Bacterial translation initiation factor IF1 is an S1 domain protein that belongs to the oligomer binding (OB) fold proteins. Cold shock domain (CSD)-containing proteins such as CspA (the major cold shock protein of Escherichia coli) and its homologues also belong to the OB fold protein family. The striking structural similarity between IF1 and CspA homologues suggests a functional overlap between these proteins. Certain members of the CspA family of cold shock proteins act as nucleic acid chaperones: they melt secondary structures in nucleic acids and act as transcription antiterminators. This activity may help the cell to acclimatize to low temperatures, since cold-induced stabilization of secondary structures in nascent RNA can impede transcription elongation. Here we show that the E. coli translation initiation factor, IF1, also has RNA chaperone activity and acts as a transcription antiterminator in vivo and in vitro. We further show that the RNA chaperone activity of IF1, although critical for transcription antitermination, is not essential for its role in supporting cell growth, which presumably functions in translation. The results thus indicate that IF1 may participate in transcription regulation and that cross talk and/or functional overlap may exist between the Csp family proteins, known to be involved in transcription regulation at cold shock, and S1 domain proteins, known to function in translation.

Published ahead of print on 23 March 2007.