The chaperonin GroEL and other heat-shock proteins, besides DnaK, participate in ribosome biogenesis in Escherichia coli

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 degrees C.

DnaK-facilitated ribosome assembly inEscherichia colirevisited

“…We see an alternative explanation based on the following findings: (1) Binding of the primary (such as S4) and secondary ribosomal proteins to the nascent 16S rRNA is DnaK-independent over a wide range of temperatures tested (El Hage et al 2001). (2) S4 is a translational autorepressor such that overexpression will decrease expression of other ribosomal proteins in the same operon (Zengel and Lindahl 1994) and also will stimulate rRNA synthesis (Takebe et al 1985;Torres et al 2001).…”

“…Such factors should be necessary to circumvent the heat-dependent conformational change of ribosomal precursor intermediates required during in vitro reconstitution of ribosomes (Nierhaus 1991;Williamson 2003). The chaperones DnaK/DnaJ/GrpE (Alix and Guerin 1993;Sbai and Alix 1998) and GroEL/GroES (El Hage et al 2001) are prime candidates for such a function, but their role, direct or not, in ribosome assembly is still mysterious. A defective DnaK system does not affect ribosome assembly at 30°C but seriously disturbs assembly at temperatures above 35°C (El Hage et al 2001).…”

“…The chaperones DnaK/DnaJ/GrpE (Alix and Guerin 1993;Sbai and Alix 1998) and GroEL/GroES (El Hage et al 2001) are prime candidates for such a function, but their role, direct or not, in ribosome assembly is still mysterious. A defective DnaK system does not affect ribosome assembly at 30°C but seriously disturbs assembly at temperatures above 35°C (El Hage et al 2001). In vitro reconstitution of ribosomes at different temperatures in the presence or absence of chaperones offers a tool to explore the role of chaperones, and has been recently exploited (Maki et al 2002).…”

DNA Memory and Input/Output

“…Furthermore, the self-assembly protocol is finicky and nonphysiological. In vitro assembly of the 30S subunit under physiological temperatures has been attained recently by adding the DnaK/DnaJ/GrpE chaperone system (Maki and Culver, 2005), although this system is dispensable in vivo (El Hage et al, 2001). Perhaps addition of natural polyamines might overcome the requirement for an unphysiologically high concentration of magnesium ions.…”

“…This will test for dependence on folding by chaperones and on posttranslational modifications. It is unclear which, if any, chaperones will be necessary, but GroEL/ES (El Hage et al, 2001;Kerner et al, 2005) are likely candidates (Table A1). …”