The chaperonin GroEL and other heat-shock proteins, besides DnaK, participate in ribosome biogenesis in Escherichia coli
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O R I GI N A L P A P E R
A. El Hage á M. SbaõÈ á J.-H. Alix
The chaperonin GroEL and other heat-shock proteins, besides DnaK, participate in ribosome biogenesis in Escherichia coli
Received: 8 June 2000 / Accepted: 25 August 2000 / Published online: 4 November 2000 Ó Springer-Verlag 2000
Abstract It has been shown that in Escherichia coli the chaperone DnaK is necessary for the late stages of 50S and 30S ribosomal subunit assembly in vivo. Here we focus on the roles of other HSPs (heat-shock proteins), including the chaperonin GroEL, in addition to DnaK, in ribosome biogenesis at high temperature. GroEL is shown to be required for the very late 45S ® 50S step in the biogenesis of the large ribosome subunit, but not for 30S assembly. Interestingly, overproduction of GroES/ GroEL can partially compensate for a lack of DnaK/ DnaJ at 44 °C. Key words DnaK/J chaperones á GroES/EL chaperonins á Ribosome biogenesis á Heat-shock proteins á Escherichia coli
Introduction Various genetic and biochemical data indicate that extra-ribosomal factors or chaperones are likely to be involved in the biogenesis of the E. coli ribosome in vivo (Alix 1993); for example, total reconstitution of active prokaryotic 30S and 50S ribosomal subunits is possible in vitro, but only under conditions that are far from physiological. For these reasons we have undertaken a study of the possible role in ribosome formation of the most abundant chaperone in E. coli, the product of the heat-shock gene dnaK. We found that dnaK-ts mutants exhibit defects in ribosome assembly at non-permissive Communicated by K. Isono A. El Hage á M. SbaõÈ á J.-H. Alix (&) Institut de Biologie Physico-Chimique. U.P.R. 9073 du C.N.R.S., 13, rue Pierre et Marie Curie, 75005 Paris, France E-mail: [email protected] Tel.: +33-1-58415135 The ®rst two authors contributed equally to this work. This is paper No. 3 in the series ``Extrinsic Factors in Ribosome Assembly''. Paper No. 2 is ``SbaõÈ and Alix 1998''.
temperatures, leading to the accumulation of ribosomal particles that sediment at 21S (precursors of normal 30S subunits) and at 32S and 45S (precursors of normal 50S subunits). This suggests that DnaK is implicated in late steps of ribosome biogenesis (Alix and GueÂrin 1993). It remains to be shown (1) whether this eect is direct or indirect; (2) whether DnaK is implicated in this process at all temperatures or only at high temperature, and (3) whether other chaperones or HSPs whose expression is dependent on the heat-shock transcription factor r32 (Gross 1996) are also involved in ribosome biogenesis. To address these questions, we have studied ribosome assembly in vivo in E. coli mutants harboring null alleles of dnaK, or of rpoH, the gene encoding the heat-shock transcription factor r32. We show that, in addition to DnaK/DnaJ, other heat-shock proteins including the chaperonins GroES/GroEL are implicated in ribosome biogenesis at high temperature, and demonstrate that under certain conditions overproduction of these proteins can partially compensate for a lack of DnaK/Dn
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