Type Ⅲ CRISPR-Cas10 systems employ multiple immune activities to defend their hosts against invasion from mobile genetic elements(MGEs),including DNase and cyclic oligoadenylates(cOA)synthesis both of which are hoste...Type Ⅲ CRISPR-Cas10 systems employ multiple immune activities to defend their hosts against invasion from mobile genetic elements(MGEs),including DNase and cyclic oligoadenylates(cOA)synthesis both of which are hosted by the type-specific protein Cas10.Extensive investigations conducted for the activation of Cas accessory proteins by cOAs have revealed their functions in the type Ⅲ immunity,but the function of the Cas10 DNase in the same process remains elusive.Here,Lactobacillus delbrueckii subsp.Bulgaricus type Ⅲ-A(Ld)Csm system,a type Ⅲ CRISPR system that solely relies on its Cas10 DNase for providing immunity,was employed as a model to investigate the DNase function.Interference assay was conducted in Escherichia coli using two plasmids:pCas carrying the LdCsm system and pTarget producing target RNAs.The former functioned as a de facto“CRISPR host element”while the latter,mimicking an invading MGE.We found that,upon induction of immune responses,the fate of each genetic element was determined by their copy numbers:plasmid of a low copy number was selectively eliminated from the E.coli cells regardless whether it represents a de facto CRISPR host or an invader.Together,we reveal,for the first time,that the immune mechanisms of Cas10 DNases are of two folds:the DNase activity is capable of removing low-copy invaders from infected cells,but it also leads to abortive infection when the invader copy number is high.展开更多
基金supported by grants from the National Key R&D Pro-gram of China(2021YFA0717000)the National Natural Science Foun-dation of China(31771380)to QS+2 种基金from the China Postdoctoral Sci-ence Foundation(2020M672050)the Qingdao Applied Research Fund For Postdoctoral Researchers(62450079311107)to ZYan Open Project from the State Key Laboratory of Microbial Technology at Shan-dong University.
文摘Type Ⅲ CRISPR-Cas10 systems employ multiple immune activities to defend their hosts against invasion from mobile genetic elements(MGEs),including DNase and cyclic oligoadenylates(cOA)synthesis both of which are hosted by the type-specific protein Cas10.Extensive investigations conducted for the activation of Cas accessory proteins by cOAs have revealed their functions in the type Ⅲ immunity,but the function of the Cas10 DNase in the same process remains elusive.Here,Lactobacillus delbrueckii subsp.Bulgaricus type Ⅲ-A(Ld)Csm system,a type Ⅲ CRISPR system that solely relies on its Cas10 DNase for providing immunity,was employed as a model to investigate the DNase function.Interference assay was conducted in Escherichia coli using two plasmids:pCas carrying the LdCsm system and pTarget producing target RNAs.The former functioned as a de facto“CRISPR host element”while the latter,mimicking an invading MGE.We found that,upon induction of immune responses,the fate of each genetic element was determined by their copy numbers:plasmid of a low copy number was selectively eliminated from the E.coli cells regardless whether it represents a de facto CRISPR host or an invader.Together,we reveal,for the first time,that the immune mechanisms of Cas10 DNases are of two folds:the DNase activity is capable of removing low-copy invaders from infected cells,but it also leads to abortive infection when the invader copy number is high.
