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Journal of Bacteriology, June 2000, p. 3377-3382, Vol. 182, No. 12
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

A Mutation in secY That Causes Enhanced SecA Insertion and Impaired Late Functions in Protein Translocation

Gen Matsumoto, Takayuki Homma, Hiroyuki Mori, and Koreaki Ito*

Institute for Virus Research, Kyoto University, Kyoto 606-8507, Japan

Received 20 December 1999/Accepted 21 March 2000

A cold-sensitive secY mutant (secY125) with an amino acid substitution in the first periplasmic domain causes in vivo retardation of protein export. Inverted membrane vesicles prepared from this mutant were as active as the wild-type membrane vesicles in translocation of a minute amount of radioactive preprotein. The mutant membrane also allowed enhanced insertion of SecA, and this SecA insertion was dependent on the SecD and SecF functions. These and other observations suggested that the early events in translocation, such as SecA-dependent insertion of the signal sequence region, is actually enhanced by the SecY125 alteration. In contrast, since the mutant membrane vesicles had decreased capacity to translocate chemical quantity of pro-OmpA and since they were readily inactivated by pretreatment of the vesicles under the conditions in which a pro-OmpA translocation intermediate once accumulated, the late translocation functions appear to be impaired. We conclude that this periplasmic secY mutation causes unbalanced early and late functions in translocation, compromising the translocase's ability to catalyze multiple rounds of reactions.

* Corresponding author. Mailing address: Institute for Virus Research, Kyoto University Sakyo-ku, Kyoto 606-8507, Japan. Phone: 81-75-751-4015. Fax: 81-75-771-5699 or 81-75-761-5626. E-mail: kito{at}virus.kyoto-u.ac.jp.

Journal of Bacteriology, June 2000, p. 3377-3382, Vol. 182, No. 12
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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