From DNA to mRNA
From mRNA to protein
NUCLEUS
CYTOPLASM
Nearly
completed
protein
NUCLEAR
MEMBRANE
Newly formed
messenger RNA
exits nucleus
mRNA
Beginning
of protein-
coding region
Double
helix
unwinds
Ribosome
mRNA
strand
C
GC
G
G
U
G
G
U
U
A
G
CG
G
G
A
G
C
A
C
C
A
A
T
C
C
T
C
C
DNA
strand
Codon for
unnatural
amino acid
Inside the ribosome
Amino acid binds to
growing protein chain
Unnatural
amino acid
Newly formed
protein chain
Ribosome Special tRNA tRNA binds to codon Codon
Glycine
mRNA
Making proteins Cells make proteins— chains of amino acids —by decoding instructions stored in dna (left). Messenger Rna copies three-letter
“words” spelled out by dna bases and then migrates outside the cell nucleus to ribosomes (inset), which assemble amino acids corresponding to the
words spelled out by the code. by reprogramming one word (pink), scientists can trick the ribosome into inserting an artificial amino acid into the chain.
of Harvard University and colleagues
described last year in Nature still another
way to get around genetic programming.
His method has the potential to rewrite
many three-letter codes at once. Just
as different words can signify the same
thing — cash, bucks and moola all mean
money — most amino acids use more than
one code. For example, the sequences
GUU, GUC, GUA and GUG all code for
the amino acid valine. Church’s laboratory has developed technology that can
erase duplicate codes — say, GUU — and
rewrite them for a custom amino acid.
“We can’t invent a new set of three letters,” Church says, “but we can knock out
the ones we want.” Once the code loses its
original meaning, the scientists are free
to rewrite it as they choose.
Now that researchers have shown that
altering the genetic code is possible, they
must ask themselves whether doing so
serves any purpose. After all, the cur-
rent code is the product of nearly 4 bil-
lion years of trial and error. Wouldn’t the
best amino acids and the best proteins be
left standing?
