초록
<P><B>ABSTRACT</B><P> Ultrahigh-molecular-weight poly[( <I>R</I> )-3-hydroxybutyrate] [UHMW-P(3HB)] synthesized by genetically engineered Escherichia coli is an environmentally friendly bioplastic material which can be processed into strong films or fibers. An operon of three genes (organized as <I>phaCAB</I> ) encodes the essential proteins for the production of P(3HB) in the native producer, Ralstonia eutropha . The three genes of the <I>phaCAB</I> operon are <I>phaC</I> , which encodes the polyhydroxyalkanoate (PHA) synthase, <I>phaA</I> , which encodes a 3-ketothiolase, and <I>phaB</I> , which encodes an acetoacetyl coenzyme A (acetoacetyl-CoA) reductase. In this study, the effect of gene order of the <I>phaCAB</I> operon ( <I>phaABC</I> , <I>phaACB</I> , <I>phaBAC</I> , <I>phaBCA</I> , <I>phaCAB</I> , and <I>phaCBA</I> ) on an expression plasmid in genetically engineered E. coli was examined in order to determine the best organization to produce UHMW-P(3HB). The results showed that P(3HB) molecular weights and accumulation levels were both dependent on the order of the <I>pha</I> genes relative to the promoter. The most balanced production result was achieved in the strain harboring the <I>phaBCA</I> expression plasmid. In addition, analysis of expression levels and activity for P(3HB) biosynthesis enzymes and of P(3HB) molecular weight revealed that the concentration of active PHA synthase had a negative correlation with P(3HB) molecular weight and a positive correlation with cellular P(3HB) content. This result suggests that the level of P(3HB) synthase activity is a limiting factor for producing UHMW-P(3HB) and has a significant impact on P(3HB) production. </P></P>