Genomic studies with Salmonella enterica serovar Typhimurium reveal a crucial role of horizontal gene transfer (HGT) in the acquisition of accessory cellular functions involved in host-interaction. Many virulence genes are located in genomic islands, plasmids and prophages. GreA and GreB proteins, Gre factors, interact transiently with the RNA polymerase alleviating backtracked complexes during transcription elongation. The overall effect of Gre factors depletion in Salmonella expression profile was studied. Both proteins are functionally redundant since only when both Gre factors were depleted a major effect in gene expression was detected. Remarkably, the accessory gene pool is particularly sensitive to the lack of Gre factors, with 18.6% of accessory genes stimulated by the Gre factors versus 4.4% of core genome genes. Gre factors involvement is particularly relevant for the expression of genes located in genomic islands. Our data reveal that Gre factors are required for the expression of accessory genes.

对肠沙门氏菌鼠伤寒血清型的基因组研究揭示了水平基因转移（HGT）在获得参与宿主相互作用的辅助细胞功能中的关键作用。许多毒力基因位于基因组岛、质粒和原噬菌体中。GreA 和 GreB 蛋白（Gre 因子）与 RNA 聚合酶短暂相互作用，减轻转录延伸过程中复合物的回溯。研究了沙门氏菌表达谱中 Gre 因子缺失的总体影响。这两种蛋白质在功能上都是冗余的，因为只有当两种 Gre 因子都被耗尽时，才会检测到基因表达的主要影响。值得注意的是，辅助基因库对 Gre 因子的缺乏特别敏感，18.6% 的辅助基因受到 Gre 因子的刺激，而核心基因组基因的这一比例为 4.4%。Gre 因子的参与与位于基因组岛的基因的表达特别相关。我们的数据表明，Gre 因子是辅助基因表达所必需的。