2017年11月15日，我院孙宝林教授研究组在美国微生物学会开放期刊mSphere发表研究论文：Chromosomal Targeting by the Type III-A CRISPR-Cas System Can Reshape Genomes in Staphylococcus aureus
作 者：Jing Guan, Wanying Wang, Baolin Sun
Abstract : CRISPR-Cas (clustered regularly interspaced short palindromic repeats [CRISPR]-CRISPR associated proteins) systems can provide protection against invading genetic elements by using crRNAs as a guide to locate and degrade the target DNA. CRISPR-Cas systems have been classified into two classes and five types according to the content of cas genes. Previous studies have indicated that CRISPR-Cas systems can avoid viral infection and block plasmid transfer. Here we show that chromosomal targeting by the Staphylococcus aureus type III-A CRISPR-Cas system can drive large-scale genome deletion and alteration within integrated staphylococcal cassette chromosome mec (SCCmec). The targeting activity of the CRISPR-Cas system is associated with the complementarity between crRNAs and protospacers, and 10 to 13 nucleotides truncation of spacers partially blocks CRISPR attack and more than 13 nucleotides truncation can fully abolish targeting, suggesting that a minimal length is required to license cleavage. Avoiding base pairings in the upstream region of protospacers is also necessary for CRISPR targeting. Successive trinucleotide complementarity between the 5’ tag of crRNAs and protospacers can disrupt targeting. Our findings reveal that type III-A CRISPR-Cas systems can modulate bacterial genome stability and may serve as a high-efficiency tool for deleting resistance or virulence genes in bacteria.