The type Ⅱ toxin-antitoxin genes are responsible for the phenotypic switch to a quasi-dormant state that enables cell survival under stresses,a similar function to heterocyst of cyanobacteria. In this paper,we particularly study the role of gene pair all3211-asl3212 under Spectinomycin stress to reveal how the type Ⅱ toxin-antitoxin involved in environmental stress responses. Bioinformatics prediction shows that toxin protein gene All3211 is homologous to Maz F,a member of maz EF family that encoding nucleases. We clone gene all3211-asl3212 into expression vectors to identify its molecular characteristics. Deletion mutant strains of all3211-asl3212 are selected in a tri-parental mating screen. Phenotype comparisons of mutant and wild type reveals no difference of single-deletion-mutants in pigment integrity,the sensitivity to antibiotics,and heterocyst formation. The results show that deletion mutation of single TAS gene pair all3211-asl3212 results in limited effects on the cellular growth of PCC 7120. Thus,we suggest that dosage compensating might be provided from redundant genes or bypass pathways to offset obvious phenotypic differences.
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