Uptake of free phage DNA by $\underline{E}. \underline{coli}$ can only be achieved when the recipient cells have been "Competent" either by turning them into spheroplast or by heat shock in the presence of calcium ion.
The degree of transfection was varied with the changes in the DNA concentration, cell concentration and cell condition. Transfection degree profile showed a saturation mode with varied concentration of challenging charon 4 phage DNA.
It is supposed that DNA is transported through cell membrane by a carrier-mediated process. Calcium ion cuases the change of cell surface or structure of cell membrane; challenging DNA can bind the carrier which has been exposured by the change of cell membrane structure.
Although the nature of the carrier is uncertain, it is obvious that a portion of charon 4 phage DNA might be involved in the binding with the $\underline{E}. \underline{coli}$ membrane protein. The affinity constant for phage DNA was estimated to be about 0.263 nM.
Energy requirement for the uptake of pahge DNA is still ambiguous, but it is supposed that the major driving force for the transfection of DNA will be provided by heat shock process.
DNA가 $\underline{E}. \underline{coli}$ 세포막을 통과하여 내부로 전달되기 위해서 세포벽을 제거하든가 $Ca^{2+}$ 존재하에서 급작스러운 온도변화 (0℃에서 42℃로)를 주어야 한다. DNA을 박테리아 속으로 통과시키는 것은 유전공학에 있어 필수적인 단계이며 본 논문에서는 DNA 통과기작과 $Ca^{2+}$역활, 온도변화의 역활등에 관하여 연구하였다.
DNA가 세포막을 통과할 때 DNA binding site 가 존재하여 DNA 는 carrier - mediated process로 통과 한다고 추측되며 carrier의 component 성질에 관하여서는 확실히 알려지지 않았다. 이때 $Ca^{2+}$은 세포막의 구조를 변화시키거나 막외부의 어떤 component를 변화시켜 DNA가 binding site 와 결합할수 있게 하며DNA 의 affinity constant $k_D$ 값은 충분한 $Ca^{2+}$ 가 존재할때 0.263nM정도로 추정한다. DNA 통과시 필요한 energy의 성질에 관하여서는 알려지지 않았으나 heat shock에 의한 것이라고 생각한다.
