Hey list.
Just thought this was interesting but I couldn't access the implications
for evolution page.
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from this week in science mailer
It would seem that proteins make the world of the cell go around. They
regulate the intake of nutrients, some of which are combusted to produce
energy; other nutrients are used as building blocks to make genetic
components such as DNA and RNA or to make structural and storage materials
such as lipids and carbohydrates. All of these processes are catalyzed by
proteins. Now we learn that proteins themselves are made in the ribosome, a
large complex of proteins and RNA, by reactions catalyzed by ribosomal RNA
(rRNA). The high-resolution structure of the large subunit of the ribosome
is described by Ban et al. (p. 905). This subunit, made of approximately
3000 ribonucleotides and 30 distinct proteins, catalyzes the synthesis of
the peptide bond, which is the linkage that joins amino acids in proteins.
The active site for this reaction is entirely surrounded by rRNA; the main
role of the protein components appears to be that of lending structural
stability. The structure of the subunit complexed with substrate analogs,
described by Nissen et al. (p. 920; see the cover), confirms that the
substrate binding-site interactions are mediated by rRNA. A universally
conserved adenine base is positioned to act as a general acid-base catalyst
for the synthesis reaction. The role of this adenine is further
characterized by Muth et al. (p. 947). It displays a substantial shift in
its acidity constant as a result of its near-neighbor interactions within
the active site (a catalytic resource thought previously to be possessed
only by proteins). The biochemical aspects of the proposed mechanism (which
appears indistinguishable from that of serine proteases, except that it
acts in reverse) and evolutionary implications are discussed in a
Perspective by Cech.
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