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PEDS Advance Access originally published online on January 11, 2007
Protein Engineering Design and Selection 2007 20(1):1-5; doi:10.1093/protein/gzl047
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© The Author 2007. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org

Bacteriophage Mu C protein is a new member of unusual leucine zipper-HTH class of proteins

Atanu Chakraborty1, Bindu Diana Paul2 and Valakunja Nagaraja1,3,4

1 Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore 560 012, India 2 Laboratory of Gene Regulation and Development, National Institute of Child Health and Human Development, National Institute of Health, Bethesda, MD 20892, USA 3 Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India

4 To whom correspondence should be addressed. E-mail: vraj{at}mcbl.iisc.ernet.in

Transcription activator protein C of bacteriophage Mu activates transcription of the late genes, including mom, during the lytic cycle of the phage. C binding to its site leads to the alteration in DNA topology of the promoter elements resulting in RNA polymerase (RNAP) recruitment. At the next step, the transactivator enhances promoter clearance of RNAP from Pmom. The C protein binds DNA with a very high affinity using a carboxyl-terminal helix turn helix (HTH) motif which has similarity with the HTH from paired domain of Drosophila prd protein. Previous studies established that the protein is dimeric in free and DNA bound forms. We describe now the unique dimerization interface of the protein. Two heptad repeats of hydrophobic amino acids found in the protein were considered to be the candidates for dimerization region. Site-directed mutational analysis revealed that the amino-terminal coiled coil region is not the dimerization determinant. In contrast, similar mutagenesis studies indicated a role for the leucine zipper motif, located in the middle region of the protein, in dimerization. Mixed oligomerization assays confirmed the importance of leucine zipper in C dimer formation establishing the presence of an uncommon zipper-HTH domain in the transactivator.

Keywords: C protein/helix turn helix/leucine zipper/phage Mu/transcription activation

Received June 28, 2006; revised September 24, 2006; accepted October 3, 2006.


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