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Cell-free
expression of protein nano-structures
As an approach to artificial gene expression systems that
could exhibit structural functions we used a cell-free
transcription/translation system to synthesize structural proteins of
the T4 bacteriophage. We focused on two proteins that participate in the
formation of the virus tail tube assembly. Synthesized separately, the
proteins assembled into their in vivo forms, namely one polymerized into
rigid hollow nanotubes 20 nm thick and hundreds of nanometers long, the
other assembled into 10 nm tubecapping hexameric rings. Co-synthesis of
the two proteins, however, revealed a novel structure of a nanodoughnut
with an outer diameter of 50 nm and thickness of 20 nm. Cell-free
co-synthesis and assembly of T4 structural proteins can be extended in a
combinatorial fashion. The addition of other structural genes offers
control of native nanoassemblies and may reveal ones not observable by
mixing purified components.
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