Durmaz E, Higgins D L, Klaenhammer T R
Department of Food Science North Carolina State University, Raleigh 27695-7624.
J Bacteriol. 1992 Nov;174(22):7463-9. doi: 10.1128/jb.174.22.7463-7469.1992.
The fifth phage resistance factor from the prototype phage-insensitive strain Lactococcus lactis subsp. lactis ME2 has been characterized and sequenced. The genetic determinant for Prf (phage resistance five) was subcloned from the conjugative plasmid pTN20, which also encodes a restriction and modification system. Typical of other abortive resistance mechanisms, Prf reduces the efficiency of plaquing to 10(-2) to 10(-3) and decreases the plaque size and burst size of the small isometric-headed phage p2 in L. lactis subsp. lactis LM0230. However, normal-size plaques occurred at a frequency of 10(-4) and contained mutant phages that were resistant to Prf, even after repeated propagation through a sensitive host. Prf does not prevent phage adsorption or promote restriction and modification activities, but 90% of Prf+ cells infected with phage p2 die. Thus, phage infections in Prf+ cells are aborted. Prf is effective in both L. lactis subsp. lactis and L. lactis subsp. cremoris strains against several small isometric-headed phages but not against prolate-headed phages. The Prf determinant was localized by Tn5 mutagenesis and subcloning. DNA sequencing identified a 1,056-nucleotide structural gene designated abiC. Prf+ expression was obtained when abiC was subcloned into the lactococcal expression vector pMG36e. abiC is distinct from two other lactococcal abortive phage resistance genes, abiA (Hsp+, from L. lactis subsp. lactis ME2) and abi416 (Abi+, from L. lactis subsp. lactis IL416). Unlike abiA, the action of abiC does not appear to affect DNA replication. Thus, abiC represents a second abortive system found in ME2 that acts at a different point of the phage lytic cycle.
来自典型的噬菌体不敏感菌株乳酸乳球菌乳酸亚种ME2的第五种噬菌体抗性因子已被鉴定并测序。Prf（噬菌体抗性五）的遗传决定因子从接合质粒pTN20亚克隆而来，该质粒还编码一种限制与修饰系统。与其他流产抗性机制一样，Prf将噬菌斑形成效率降低至10^(-2)到10^(-3)，并减小乳酸乳球菌乳酸亚种LM0230中小等轴头噬菌体p2的噬菌斑大小和爆发量。然而，正常大小的噬菌斑以10^(-4)的频率出现，并且包含对Prf具有抗性的突变噬菌体，即使在通过敏感宿主反复传代后也是如此。Prf并不阻止噬菌体吸附，也不促进限制与修饰活性，但90%感染噬菌体p2的Prf+细胞会死亡。因此，Prf+细胞中的噬菌体感染会流产。Prf对乳酸乳球菌乳酸亚种和乳酸乳球菌乳脂亚种的几种小等轴头噬菌体均有效，但对长头噬菌体无效。通过Tn5诱变和亚克隆确定了Prf决定因子的位置。DNA测序鉴定出一个1056个核苷酸的结构基因，命名为abiC。当abiC亚克隆到乳球菌表达载体pMG36e中时可获得Prf+表达。abiC与另外两个乳球菌流产噬菌体抗性基因abiA（来自乳酸乳球菌乳酸亚种ME2的Hsp+）和abi416（来自乳酸乳球菌乳酸亚种IL416的Abi+）不同。与abiA不同，abiC的作用似乎不影响DNA复制。因此，abiC代表了在ME2中发现的第二种流产系统，其作用于噬菌体裂解周期的不同点。
