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Molecular and Cellular Biology, October 1999, p. 6575-6584, Vol. 19, No. 10
Department of Biological Sciences,
Received 8 March 1999/Returned for modification 13 April
1999/Accepted 29 June 1999
We have isolated the RPN9 gene by two-hybrid screening
with, as bait, RPN10 (formerly SUN1), which
encodes a multiubiquitin chain receptor residing in the regulatory
particle of the 26S proteasome. Rpn9 is a nonessential subunit of the
regulatory particle of the 26S proteasome, but the deletion of this
gene results in temperature-sensitive growth. At the restrictive
temperature, the
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
Rpn9 Is Required for Efficient Assembly of the Yeast 26S
Proteasome
rpn9 strain accumulated
multiubiquitinated proteins, indicating that the RPN9
function is needed for the 26S proteasome activity at a higher
temperature. We analyzed the proteasome fractions separated by glycerol
density gradient centrifugation by native polyacrylamide gel
electrophoresis and found that a smaller amount of the 26S proteasome
was produced in the
rpn9 cells and that the 26S
proteasome was shifted to lighter fractions than expected. The
incomplete proteasome complexes were found to accumulate in the
rpn9 cells. Furthermore, Rpn10 was not detected in the
fractions containing proteasomes of the
rpn9 cells.
These results indicate that Rpn9 is needed for incorporating Rpn10 into
the 26S proteasome and that Rpn9 participates in the assembly and/or
stability of the 26S proteasome.
*
Corresponding author. Mailing address: Department of
Biological Sciences, Graduate School of Science, University of Tokyo, Hongo, Tokyo 113-0033, Japan. Phone and Fax: 81-3-5684-9420. E-mail: toh-e{at}biol.s.u-tokyo.ac.jp.
Molecular and Cellular Biology, October 1999, p. 6575-6584, Vol. 19, No. 10
0270-7306/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
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