coli strains upon changes in growth temperature [13]. Expression of FabF1 restored cis-vaccenate synthesis at all temperatures,

but was much more effective at 30°C than at 37°C or 42°C (Table 1). This effect seems likely to be due to the effects of temperature on FabF1 synthase activity since thermal regulation disappeared upon X-396 manufacturer expression of FabF1 from a high copy number vector (Table 1) and the enzyme was thermolabile in vitro (see below). Apparently, at high growth temperatures low levels FabF1 elongation activity was overcome by high-level expression of the protein. We also found high levels of cis-vaccenate at the non-permissive temperature upon expression of fabF1 in an E. coli fabB fabF strain that carried the fabB gene of Haemophilus influenzae, INCB024360 cost a bacterium naturally defective in both cis-vaccenate synthesis and in regulation of fatty acid composition by temperature [14] (data not shown).

Table 1 Effects of growth temperature on fatty acid compositions (% by weight)of fabF strain MR52 carrying plasmids encoding C. acetobutylicium fabF1.   30°C 37°C 42°C Fatty acid pHW33 pHW36 pHW33 pHW36 pHW33 pHW36 C14:0 2.2 5.8 2.4 6.2 2.6 3.3 C16:1 40.3 29 35 24.8 53.4 28.9 C16:0 21.4 25.8 32.4 25.1 26.2 28.7 C18:1 33.3 30 25.9 32.4 14.8 30.2 C18:0 2.8 9.4 4.3 11.6 2.9 8.7 Figure 2 Growth of E. coli strains CY242, K1060, CY244, and JWC275 transformed with plasmids encoding the C. acetobutylicium fabF homologues. Following induction by addition of arabinose, transformants of strain K1060 were grown at 37°C, whereas the transformants of strains CY242, strain CY244 and strain JWC275 were grown at 42°C. The strains carried plasmids pHW36, pHW37 or pHW38 encoding fabF1, fabF2 and fabF3, respectively, or the vector plasmid, pBAD24. The C. acetobutylicium fabF1 gene can functionally replace

E. coli FabB Although the presence of plasmid pHW36 (fabF1) PJ34 HCl allowed growth of the two E. coli fabB(Ts) fabF strains at the non-permissive temperature, growth of both strains required oleate. The lack of growth in the absence of oleate argued that either FabF1 lacked the ability to replace FabB or that FabF1 was unable to simultaneously perform the tasks of both FabB and FabF under these conditions. To decide between these alternatives we transformed pHW36 into strain K1060, a strain that carries an unconditional fabB allele, and into strain CY242 which carries the same fabB(Ts) allele as strain CY244. The complementation experiments showed that C. acetobutylicium fabF1 allowed strain K1060 to grow on RB medium lacking oleate at 37°C (Fig. 2). However, fabF1 failed to complement growth of the temperature sensitive fabB mutant strain, CY242 at 42°C (Fig. 2). If FabF1 possessed FabB activity at 37°C, unsaturated fatty acids should be synthesized.