Factors of Lactobacillus casei which inhibit plasmid replication

通过用盐溶液（pH 8.6）洗涤干酪乳杆菌获得的提取物含有抑制质粒RP 4复制的未知抑制剂。提取物通过Sephadex G25凝胶过滤分离成几个级分。当在pH 4.8下进行凝胶过滤时，分子量为500或更小的级分显示出抑制活性。该级分（Lu）非常不稳定，并且含有尿嘧啶作为主要组分和一些其他核苷酸。当在pH 7.0下进行凝胶过滤时，分子量对应于1，000的级分含有稳定的抑制活性。该级分（Ls）不具有核苷酸或氨基酸作为主要成分。Ls组分对质粒RP 4和Ent-质粒的复制显示出抑制作用，但对高拷贝的质粒如质粒pBR 322没有抑制作用。我们还研究了测定质粒拷贝的分析方法，并得出结论，最好的方法是用[ &lt;^（32）P&gt; ]<H_3><PO_4>代替[ &lt;^3H&gt; ]胸苷标记。

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.