JBC, Vol. 251, Issue 4, 1147-1153, Feb, 1976
The site of ribosome degradation in starved Escherichia coli cells
R. Kaplan and E. Hartstein
An attempt was made, in starved Escherichia coli cells, to locate the site
at which the process of ribosome degradation is initiated. Supernatant and
rapidly sedimenting pellet fractions from exponentially growing and from
carbon-starved cells were prepared, and the ribonucleic acids from these
fractions were seperated by polyacrylamide electrophoresis and quantitated.
The data indicated that 23 S, 16 S, and 5 S RNA are lost only from the
pellet; and also that the low molecular weight RNA degradation products are
confined to this fraction. Ribosomes from supernatant and pellet fractions
were seperated on sucrose density gradients. The sedimentation profiles
obtained indicated that pellet fractions of starved cells contain for the
most part 50 S and 30 S subunits, whereas 70 S monosomes were most abundant
in the supernatant fraction. In vitro measurements on RNA degradation in
supernatant and rapidly sedimenting pellet fractions confirmed the in vivo
data on the exclusive degradation of ribosomal RNA in the pellet. Based on
these data and on previous observations, we suggest that the
endoribonucleolytic attack which triggers ribosome degradation, occurs in
free subunits attached to the rapidly sedimenting membrane fraction.
Subsequently, the ribosome falls apart, and the small RNA pieces generated
remain attached to the pellet fraction until their final degradation by the
exonuclease.
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