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Journal of Bacteriology, November 2007, p. 7618-7625, Vol. 189, No. 21
0021-9193/07/$08.00+0     doi:10.1128/JB.00854-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The T4 RI Antiholin Has an N-Terminal Signal Anchor Release Domain That Targets It for Degradation by DegP{triangledown}

Tram Anh T. Tran, Douglas K. Struck, and Ry Young*

Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, Texas 77843-2128

Received 1 June 2007/ Accepted 26 July 2007

Lysis inhibition (LIN) of T4-infected cells was one of the foundational experimental systems for modern molecular genetics. In LIN, secondary infection of T4-infected cells results in a dramatically protracted infection cycle in which intracellular phage and endolysin accumulation can continue for hours. At the molecular level, this is due to the inhibition of the holin, T, by the antiholin, RI. RI is only 97 residues and contains an N-terminal hydrophobic domain and a C-terminal hydrophilic domain; expression of the latter domain fused to a secretory signal sequence is sufficient to impose LIN, due to its specific interaction with the periplasmic domain of the T holin. Here we show that the N-terminal sequence comprises a signal anchor release (SAR) domain, which causes the secretion of RI in a membrane-tethered form and then its subsequent release into the periplasm, without proteolytic processing. Moreover, the SAR domain confers both functional lability and DegP-mediated proteolytic instability on the released form of RI, although LIN is not affected in a degP host. These results are discussed in terms of a model for the activation of RI in the establishment of the LIN state.

* Corresponding author. Mailing address: Department of Biochemistry and Biophysics, Texas A&M University, 2128 TAMU, College Station, TX 77843-2128. Phone: (979) 845-2087. Fax: (979) 862-4718. E-mail: ryland{at}tamu.edu

{triangledown} Published ahead of print on 10 August 2007.

Journal of Bacteriology, November 2007, p. 7618-7625, Vol. 189, No. 21
0021-9193/07/$08.00+0     doi:10.1128/JB.00854-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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