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Journal of Bacteriology, August 1999, p. 4561-4567, Vol. 181, No. 15
Genetics and Biochemistry Branch, National
Institute of Diabetes and Digestive and Kidney Diseases, National
Institutes of Health, Bethesda, Maryland 20892
Received 1 April 1999/Accepted 25 May 1999
The signal recognition particle (SRP) targeting pathway is required
for the efficient insertion of many polytopic inner membrane proteins
(IMPs) into the Escherichia coli inner membrane, but in the
absence of SRP protein export proceeds normally. To define the
properties of IMPs that impose SRP dependence, we analyzed the
targeting requirements of bitopic IMPs that are structurally intermediate between exported proteins and polytopic IMPs. We found
that disruption of the SRP pathway inhibited the insertion of only a
subset of bitopic IMPs. Studies on a model bitopic AcrB-alkaline phosphatase fusion protein (AcrB 265-AP) showed that the SRP
requirement for efficient insertion correlated with the presence of a
large periplasmic domain (P1). As previously reported, perturbation of
the SRP pathway also affected the insertion of a polytopic AcrB-AP
fusion. Even exhaustive SRP depletion, however, failed to block the
insertion of any AcrB derivative by more than 50%. Taken together,
these data suggest that many proteins that are normally targeted by SRP
can utilize alternative targeting pathways and that the structure of
both hydrophilic and membrane-spanning domains determines the degree to
which the biogenesis of a protein is SRP dependent.
0021-9193/99/$04.00+0
The Structure of Multiple Polypeptide Domains
Determines the Signal Recognition Particle Targeting Requirement of
Escherichia coli Inner Membrane Proteins
and
*
Corresponding author. Mailing address: National
Institutes of Health, Bldg. 10, Rm. 9D-20, Bethesda, MD 20892-1810. Phone: (301) 402-4770. Fax: (301) 402-0387. E-mail:
harris_bernstein{at}nih.gov.
Current address: MedImmune, Inc., Gaithersburg, MD 20878.
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