Ribosome biogenesis is temperature-dependent and delayed in Escherichia coli lacking the chaperones DnaK or DnaJ.
In Escherichia coli strains carrying null mutations in either the dnaK or dnaJ genes, the late stages of 30S and 50S ribosomal subunit biogenesis are slowed down in a temperature-dependent manner. At high temperature (44 degrees C), 32S and 45S particles (precursors to 50S subunits) and 21S particles (precursors to 30S subunits) accumulate. The latter are shown by 3'5' rapid amplification of cDNA ends analysis to contain unprocessed or partially processed 16S ribosomal RNA at the 5' end, but the 3' end was never processed. This implies that maturation of 16S ribosomal RNA starts at the 5'-terminus, and that the 3'-terminus is only trimmed at a later step. At normal temperatures (30 degrees C-37 degrees C), ribosome assembly in both mutants is not arrested but is significantly delayed, as shown by pulse-chase analysis. Assembly defects are partially compensated by an overexpression of other heat-shock proteins, which occurs in the absence of their negative regulator DnaK, or by a plasmid-driven overexpression of GroES/GroEL, suggesting the involvement of a network of chaperones in ribosome biogenesis.
Al Refaii
Abdalla
A
CNRS UPR9073 (affiliated with University Paris 7-Denis Diderot), Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, Paris, France.
Alix
Jean-Hervé
JH
D001483:Base Sequence; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D050956:HSP40 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D018840:HSP70 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D008969:Molecular Sequence Data; D012329:RNA, Bacterial / Q000096:biosynthesis*; D012336:RNA, Ribosomal, 16S / Q000096:biosynthesis; D012270:Ribosomes / Q000378:metabolism*
C494635:DnaJ protein, E coli; D029968:Escherichia coli Proteins; D050956:HSP40 Heat-Shock Proteins; D018840:HSP70 Heat-Shock Proteins; D012329:RNA, Bacterial; D012336:RNA, Ribosomal, 16S; C063842:dnaK protein, E coli