higher transfection efficiency than one with a low copy number origin, using a plasmid with an origin of replication that is active in the host cell can lead to a higher transfection efficiency. Transformation conditions – The method of preparation of competent cells, the length of time of heat shock, temperature of heat shock, incubation time after heat shock, growth medium used, pH and various additives, all can affect the transformation efficiency of the cells. The presence of contaminants as well as ligase in a ligation mixture can reduce the transformation efficiency in electroporation, and inactivation of ligase or chloroform extraction of DNA may be necessary for electroporation, alternatively only use a tenth of the ligation mixture to reduce the amount of contaminants. Normal preparation of competent cells can yield transformation efficiency ranging from 106 to 108 cfu/μg DNA. Protocols for chemical method however exist for making super competent cells that may yield a transformation efficiency of over 1 x 109. Damage to DNA – Exposure of DNA to UV radiation in standard preparative agarose gel electrophoresis procedure for as little as 45 seconds can damage the DNA, and this can significantly reduce the transformation efficiency. Adding cytidine or guanosine to the electrophoresis buffer at 1 mM concentration however may protect the DNA from damage. A higher-wavelength UV radiation (365 nm) which cause less damage to DNA should be used if it is necessary work for work on the DNA on a UV transilluminator for an extended period of time. This longer wavelength UV produces weaker fluorescence with the ethidium bromide intercalated into the DNA, therefore if it is necessary to capture images of the DNA bands, a shorter wavelength (302 or 312 nm) UV radiations may be used. Such exposure however should be limited to a very short time if the DNA is to be recovered later for ligation and transformation. Efficiency of transformation methods The method used for introducing the DNA have a significant impact on the transformation efficiency. Electroporation Electroporation tends to be more efficient than chemical methods and can be applied to a wide range of species and to strains that were previously resistant and recalcitrant to transformation techniques. Electroporation has been found to have an average yield typically between 104 - 108 CFU/ug . However , a transformation efficiencies as high as 0.5-5 x 1010 colony forming units (CFU) per microgram of DNA for E.