Factors of Lactobacillus casei which inhibit plasmid replication

用pH 8.6的盐溶液洗涤干酪乳杆菌得到的提取物中含有一种未知的抑制质粒RP4复制的抑制剂。用Sephadex G25凝胶过滤将提取物分离成几个部分。当pH值为4.8时进行凝胶过滤时，分子量为500或更小的部分显示出抑制活性。这一组分（Lu）极不稳定，主要含有尿嘧啶和其他一些核苷酸。在pH 7.0下进行凝胶过滤时，分子量为1000的部分具有稳定的抑制活性。这个部分（Ls）没有核苷酸和氨基酸作为主要成分。Ls部分对质粒RP4和ent -质粒的复制有抑制作用，但对高拷贝质粒pBR322的复制无抑制作用。我们还研究了质粒拷贝的测定方法，得出用[<^(32)P>] <H_3> <PO_4>代替[<^3H>]胸苷标记质粒拷贝的最佳方法。

The extracts obtained by washing Lactobacillus casei with salt solution (pH 8.6) contained an unknown inhibitor which inhibited replication of plasmid RP4. The extracts were separated to several fractions by gel filtration on Sephadex G25. When gel filtration was carried out at pH 4.8, a fraction of which molecular weight was 500 or less showed and an inhibitory activity. This fraction (Lu) was extremely unstable, and contained uracil as a major component and some other nucleotides. When gel filtration was carried out at pH 7.0, a fraction of which molecular weight corresponded to 1,000 contained a stable inhibitory activity. This fraction (Ls) did not have nucleotides nor amino acids as major constituents. The Ls fraction showed inhibitory effects on replication of plasmid RP4 and Ent-plasmid, but not on a plasmid of a high copy such as plasmid pBR322. We also investigated assay procedures for determination of plasmid copy, and concluded that the best way was labeling with [ <^(32)P> ] <H_3> <PO_4> instead of [ <^3H> ]thymidine.